Window.tscn was renamed to MainScreen.tscn

- New Credits window and it's respective button
- Renamed panel_height to content_height
- Window content text now supports BBCode
- Made sure the content height doesn't exceed 216 pixels
- GPL license notice now included in the about window
- SixAM splash screen

assets/sixam_splash.png.import

@@ -0,0 +1,29 @@
+[remap]
+
+importer="texture"
+type="StreamTexture"
+path="res://.import/sixam_splash.png-c58f13964bb4f1a11257474ab2e19217.stex"
+
+[deps]
+
+source_file="res://assets/sixam_splash.png"
+dest_files=[ "res://.import/sixam_splash.png-c58f13964bb4f1a11257474ab2e19217.stex" ]
+
+[params]
+
+compress/mode=0
+compress/lossy_quality=0.7
+compress/hdr_mode=0
+compress/normal_map=0
+flags/repeat=0
+flags/filter=true
+flags/mipmaps=false
+flags/anisotropic=false
+flags/srgb=2
+process/fix_alpha_border=true
+process/premult_alpha=false
+process/HDR_as_SRGB=false
+stream=false
+size_limit=0
+detect_3d=true
+svg/scale=1.0