Setup UITrees and UITreeContainers to differentiate between node selection by keyboard and by mouse. Removed ability to optionally select a node in UITreeContainer::scrollToNode() method. Removed ability to travel to first child node via right arrow key (use down).
Arrow-key nav no longer opens files in PolycodeProjectBrowser as a side-effect -- use the enter key, right arrow key, or single-click mouse.
Merge pull request #303 from TheCosmotect/projbrowser-selection

Arrow-key nav/selection no longer opens files as a side-effect in PolycodeProjectBrowser