Population Improvements

[Updownquark]

• [x] Nail down threading issues in tree (Searcher)
• [ ] Show more version information in About
• [ ] App use documentation in About (maybe just a link, see below)
• [x] Links with custom actions or browse events
• [ ] Show version information after upgrade (done, but ugly)
• [x] Make ObservableUiBuilder extension in Observe-ext that makes GitHub integration easier
• [ ] Multi-selection in trees
• [x] Sliders
• [ ] Spinners
• [x] Progress bar
• [ ] Offloaded actions (with progress on glass pane)
  • [ ] With built-in support on things like tree and table actions (especially multi-enabled) with progress bar
• [x] Menu button
• [x] Fix split pane divider location
• [ ] Scroll pane
• [ ] ObservableValueSelector
• [ ] Settings Menu (gear)
• [ ] Rotation?
• [ ] Form controls (e.g. press enter in a text field and a submit action (also tied to a button) fires)
• [ ] More draggability
• [ ] LittleList sometimes grows too much
• [ ] Splash screen support (optionally point to image from app, but optionally use the image from the cmd-line splash screen, then add progress and text)