this fixes the cubemap ressource editor bug described in issue #908.
some other littles fixes will be required to allow the Environment
ressource to create and load Cubemap Ressources more easily
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-Sprite3D and AnimatedSprite3D support.
-Opaque pre-pass works, is compatible with shadows
-Improved shadow map rendering (can differentiate between plain opaque and opaque with shaders/discard/etc)
-Added option to use alpha discard in FixedMaterial
-Improved Glow FX, many more options (three modes, Additive, Screen and SoftLight), strength and scale
-Ability for Background (image or cubemap) to send to glow buffer
-Dumb Deploy of clients now actually works in Android
-Many Many rendering fixes, 3D is much more usable now.
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-Auto indenter in code editor, this makes it much easier to paste external code.
-Zoom in 2D viewport now uses the mouse pointer as reference.
-Obscure hack to see where code/line of GDScript in C++ backtrace.
-Fixed a bug where keys would get stuck on X11 if pressed simultaneously
-Added Api on IP singleton to request local IPs.
-Premultiplied alpha support when importing texture, editing PNGs and as a blend mode.
-fixed TouchScreenButton with stretch2d
-fixed(?) OSX crash on startup (test!!)
-compilation fixes on windows
-CollisionPolygon editor works again
-find buttons en find dialog
-TileMap editor cleanup (removed "error", made nicer)
-viewport flicker fixed
-make .scn default extension for saving scenes
-export the rest of the network classes to gdscript
