Improve shader editor

[glopesdev]

Original report by Ivar Clemens (Bitbucket: ivarcl, ).

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The shader editor is difficult to use at this moment because:

• It is quite small;
• Changes are easily lost, e.g. when pressing the escape key;
• The dialog is modal, which forces the user to close it before testing the workflow.

Some possible solutions:

• Use tabs and give each shader its own textarea and make the dialog non-modal.
• Open a new (non-modal) editor window when clicking the shader in the property window.

Editing should probably be disabled while the workflow is running though.

[glopesdev]

I believe the new editor using Scintilla.NET solves most of these problems:

• Opens a dedicated dialog for the source
• Does not close on Escape and supports Undo/Redo (Ctrl+Z)
• Adds nice syntax highlighting

I decided to keep the dialogs modal for consistency with the remaining editors. I may consider in the future an option to load shaders from external files, which would then allow you to use whatever editor you prefer.

[glopesdev]

Quick update on this issue for future reference: both the shader configuration and GLSL editor windows are now modeless.