Rework I/O UI Layer

[sghpjuikit]

UX that displays widget's inputs and outputs and links has some issues and lots of potential for improvement.

I have just fixed several of these, but some remain:

• ✓ selection graphics
• ✓ data flow/arrive animations
• ✓ some links not showing
• ✓ broken layout
• ✓ support for mapped/dependent outputs and inputs
• ✓ unified widget i/o API
• ✓ value-to-list wrapping support
• ✓ per window
• ✓ input/output linking to specified default value if not overridden by user
• ✓ input/output link value only
• ✓ input/output context menu
• ✓ force-based layout for the node labels (may not work out)
• ✓ broken layout mode trigger animation
• ✓ react to widget layout changes
• ✓ minimize layout invocations
• async value passing support
• UX tooltip explaining node selection and LMB/RMB/drag actions

On the table is also special widget/mode showing virtualized view of the entire application. Once per-window is implemented, linking widgets between windows will become a problem (well, right now its impossible too). Shouldn't be too hard, will see.

[sghpjuikit]

Closing this as delivered.

I have some more ideas for the future, but current state is satisfactory. Particularly, is has full feature set, no (known) bugs, good UX.