[EXPERIMENTAL] Added ability to load a shader as an image effect

This new feature allows users to load a .shader file (must be a GLES2 Godot shader) that will modify the image itself. This feature is experimental and possibly buggy, not all shaders are working properly and I'm not sure yet why. As such, this feature may not be included in v0.8 stable.

src/UI/Dialogs/ShaderEffect.tscn

@@ -0,0 +1,86 @@
+[gd_scene load_steps=3 format=2]
+
+[ext_resource path="res://src/UI/Dialogs/ShaderEffect.gd" type="Script" id=2]
+
+[sub_resource type="ShaderMaterial" id=1]
+
+[node name="ShaderEffect" type="ConfirmationDialog"]
+margin_right = 200.0
+margin_bottom = 228.0
+rect_min_size = Vector2( 0, 0 )
+resizable = true
+script = ExtResource( 2 )
+__meta__ = {
+"_edit_use_anchors_": false
+}
+
+[node name="VBoxContainer" type="VBoxContainer" parent="."]
+anchor_right = 1.0
+anchor_bottom = 1.0
+margin_left = 8.0
+margin_top = 8.0
+margin_right = -8.0
+margin_bottom = -36.0
+__meta__ = {
+"_edit_use_anchors_": false
+}
+
+[node name="Label" type="Label" parent="VBoxContainer"]
+margin_right = 255.0
+margin_bottom = 48.0
+text = "This is an experimental feature and may not be included in the stable version"
+autowrap = true
+
+[node name="ViewportContainer" type="ViewportContainer" parent="VBoxContainer"]
+margin_top = 52.0
+margin_right = 255.0
+margin_bottom = 53.0
+__meta__ = {
+"_edit_use_anchors_": false
+}
+
+[node name="Viewport" type="Viewport" parent="VBoxContainer/ViewportContainer"]
+size = Vector2( 1, 1 )
+transparent_bg = true
+handle_input_locally = false
+disable_3d = true
+usage = 0
+render_target_update_mode = 0
+gui_disable_input = true
+
+[node name="Preview" type="TextureRect" parent="VBoxContainer/ViewportContainer/Viewport"]
+material = SubResource( 1 )
+anchor_right = 1.0
+anchor_bottom = 1.0
+
+[node name="ChooseShader" type="Button" parent="VBoxContainer"]
+margin_top = 57.0
+margin_right = 255.0
+margin_bottom = 77.0
+mouse_default_cursor_shape = 2
+text = "Choose Shader"
+
+[node name="ShaderLoadedLabel" type="Label" parent="VBoxContainer"]
+margin_top = 81.0
+margin_right = 255.0
+margin_bottom = 95.0
+text = "No shader loaded!"
+autowrap = true
+
+[node name="FileDialog" type="FileDialog" parent="."]
+margin_left = 8.0
+margin_top = 8.0
+margin_right = 263.0
+margin_bottom = 192.0
+window_title = "Open a File"
+resizable = true
+mode = 0
+access = 2
+filters = PoolStringArray( "*shader" )
+current_dir = "/Users/Overloaded/Dropbox/Orama Founding Members/εταιρικα αρχεια/Godot Projects/Pixelorama"
+current_path = "/Users/Overloaded/Dropbox/Orama Founding Members/εταιρικα αρχεια/Godot Projects/Pixelorama/"
+[connection signal="about_to_show" from="." to="." method="_on_ShaderEffect_about_to_show"]
+[connection signal="confirmed" from="." to="." method="_on_ShaderEffect_confirmed"]
+[connection signal="popup_hide" from="." to="." method="_on_ShaderEffect_popup_hide"]
+[connection signal="pressed" from="VBoxContainer/ChooseShader" to="." method="_on_ChooseShader_pressed"]
+[connection signal="file_selected" from="FileDialog" to="." method="_on_FileDialog_file_selected"]