Import brushes from folder

- A new type of custom brush has been added, brushes from files! Basically there's a "Brushes" folder where Pixelorama can get brushes from, and, unlike the previous brushes, these are for all projects and are not saved in .pxo files. These brushes get loaded on the _ready() method of Main.gd, and are ignored by Godot.
- There are now 2 containers for the two types of custom brushes. The main pixel brush is with the brushes from files.
- Fixed bug where, if you had selected a custom "project" brush and loaded a .pxo file, the brush would still be selected, causing potential problems
- Fixed bug where you could save a project brush that was completely transparent
- Fixed bug where, if you named a file, some shortcuts would be activated.
- export_presets.cfg is now ignored.

Main.tscn

@@ -23,7 +23,6 @@ size_flags_horizontal = 3
 custom_constants/separation = 0
 
 [node name="ToolPanel" type="Panel" parent="UI"]
-editor/display_folded = true
 margin_right = 230.0
 margin_bottom = 600.0
 rect_min_size = Vector2( 230, 0 )
@@ -37,10 +36,11 @@ size_flags_vertical = 3
 
 [node name="MenusAndTools" type="VBoxContainer" parent="UI/ToolPanel/Tools"]
 margin_right = 230.0
-margin_bottom = 266.0
+margin_bottom = 242.0
 size_flags_vertical = 3
 
 [node name="MenuItems" type="HBoxContainer" parent="UI/ToolPanel/Tools/MenusAndTools"]
+editor/display_folded = true
 margin_right = 230.0
 margin_bottom = 20.0
 
@@ -72,6 +72,7 @@ mouse_default_cursor_shape = 2
 text = "Help"
 
 [node name="PaintToolsContainer" type="HBoxContainer" parent="UI/ToolPanel/Tools/MenusAndTools"]
+editor/display_folded = true
 margin_top = 24.0
 margin_right = 230.0
 margin_bottom = 44.0
@@ -118,6 +119,7 @@ button_mask = 3
 text = "Bucket"
 
 [node name="ColorToolsContainer" type="HBoxContainer" parent="UI/ToolPanel/Tools/MenusAndTools"]
+editor/display_folded = true
 margin_top = 48.0
 margin_right = 230.0
 margin_bottom = 68.0
@@ -144,6 +146,7 @@ button_mask = 3
 text = "Lighten/Darken"
 
 [node name="SelectionToolsContainer2" type="HBoxContainer" parent="UI/ToolPanel/Tools/MenusAndTools"]
+editor/display_folded = true
 margin_top = 72.0
 margin_right = 230.0
 margin_bottom = 92.0
@@ -159,22 +162,21 @@ button_mask = 3
 text = "RectSelect"
 
 [node name="HSeparator" type="HSeparator" parent="UI/ToolPanel/Tools"]
-margin_top = 270.0
+margin_top = 246.0
 margin_right = 230.0
-margin_bottom = 274.0
+margin_bottom = 250.0
 
 [node name="ToolOptions" type="HBoxContainer" parent="UI/ToolPanel/Tools"]
-editor/display_folded = true
-margin_top = 278.0
+margin_top = 254.0
 margin_right = 230.0
-margin_bottom = 544.0
+margin_bottom = 496.0
 size_flags_vertical = 3
 custom_constants/separation = 0
 
 [node name="LeftToolOptions" type="VBoxContainer" parent="UI/ToolPanel/Tools/ToolOptions"]
 editor/display_folded = true
 margin_right = 113.0
-margin_bottom = 266.0
+margin_bottom = 242.0
 size_flags_horizontal = 3
 
 [node name="LeftLabel" type="Label" parent="UI/ToolPanel/Tools/ToolOptions/LeftToolOptions"]
@@ -269,13 +271,13 @@ text = "Vert. Mirror"
 [node name="VSeparator" type="VSeparator" parent="UI/ToolPanel/Tools/ToolOptions"]
 margin_left = 113.0
 margin_right = 117.0
-margin_bottom = 266.0
+margin_bottom = 242.0
 
 [node name="RightToolOptions" type="VBoxContainer" parent="UI/ToolPanel/Tools/ToolOptions"]
 editor/display_folded = true
 margin_left = 117.0
 margin_right = 230.0
-margin_bottom = 266.0
+margin_bottom = 242.0
 size_flags_horizontal = 3
 
 [node name="RightLabel" type="Label" parent="UI/ToolPanel/Tools/ToolOptions/RightToolOptions"]
@@ -367,18 +369,19 @@ margin_bottom = 218.0
 text = "Vert. Mirror"
 
 [node name="HSeparator2" type="HSeparator" parent="UI/ToolPanel/Tools"]
-margin_top = 548.0
+margin_top = 500.0
 margin_right = 230.0
-margin_bottom = 552.0
+margin_bottom = 504.0
 
 [node name="BrushesContainer" type="ScrollContainer" parent="UI/ToolPanel/Tools"]
-margin_top = 556.0
+margin_top = 508.0
 margin_right = 230.0
-margin_bottom = 592.0
+margin_bottom = 544.0
 size_flags_horizontal = 3
 scroll_vertical_enabled = false
 
 [node name="BrushHBoxContainer" type="HBoxContainer" parent="UI/ToolPanel/Tools/BrushesContainer"]
+editor/display_folded = true
 margin_right = 36.0
 margin_bottom = 36.0
 
@@ -397,6 +400,21 @@ centered = false
 offset = Vector2( 28, 0 )
 
 [node name="HSeparator3" type="HSeparator" parent="UI/ToolPanel/Tools"]
+margin_top = 548.0
+margin_right = 230.0
+margin_bottom = 552.0
+
+[node name="CustomBrushesContainer" type="ScrollContainer" parent="UI/ToolPanel/Tools"]
+margin_top = 556.0
+margin_right = 230.0
+margin_bottom = 592.0
+rect_min_size = Vector2( 0, 36 )
+size_flags_horizontal = 3
+scroll_vertical_enabled = false
+
+[node name="CustomBrushHBoxContainer" type="HBoxContainer" parent="UI/ToolPanel/Tools/CustomBrushesContainer"]
+
+[node name="HSeparator4" type="HSeparator" parent="UI/ToolPanel/Tools"]
 margin_top = 596.0
 margin_right = 230.0
 margin_bottom = 600.0