Added blend modes (Dissolve, Multiply, Screen, Overlay, Hard Light, Soft Light).
Fixed color popup position in the GradientEditor.
Fixed initial panoram shown in preview.
Now gradient editor can remove points.
Improved preview:
- added panorama to 3d preview (with panoramas from the godot material demo)
- texture preview can be maximized
- shader updates are delayed by .25 seconds to avouid UI freeze
- fixed GraphNode initialization upon loading
- started obsoleting get_source_rgb and get_source_f functions
- updated colorize node to use gradient
- image node can now be loaded/saved
- removed iqnoise node
- rewrote perlin shader to support a seed parameter (seed is calculated from the node's position, so just move it to reseed)
- Added voronoi noise node
- updated code to use % formats instead of concatenating strings (should solve type problems in shaders)
- reworked the context menu (now has submenus)
- fixes in the gradient editor
