Nionui

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- Default SVG now uses fastest compression rather than best (see nionswift-642).

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- Fix some drawing inconsistencies during splitter dragging.
- Minor improvements to drawing performance.
- Fix potential crash when closing canvas items with threads.
- Add window file path support to Window.
- Add support for directly getting last or current keyboard modifiers.
- Only change canvas item focus when no key modifiers are enabled.
- Add menu methods for adding only if enabled and checking if enabled.
- Expand action architecture to support parameters and results.
- Require sizing to be set by the canvas item (backwards incompatible).

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- Add color dialog support, a color well widget, and some color utility functions.

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- Execute context menus actions by queue to fix crashes.

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- Extend declarative list box to support item tool tips and context menu.
- Add mechanism to request window close from within event loop.

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- Add ability to determine whether a canvas item is interacting with user.
- Add ability to add actions to context menus.
- Improve look of pose dialog.