5/27/14 change 'imports' to 'modules' in require comments
8/22/13 #35, terminology change: tab -> screen
5/8/13 added credits to About dialog, temporary (Phase 1?) solution
5/8/13 Made tab name white instead of black against a white background
4/24/13 Moved home screen, tab navigation bar, about dialog, popup menu into their own divs/Scenes.  See docs in HomeScreenScene for tradeoffs.
4/23/13 rename PlayArea -> TabView, per developer meeting
4/22/13 implemented background-color switching for Tabs
4/22/2013 Moved Sim.js and related classes from repo "scenery-phet".  If you want their history before this, you will have to look over there.