Upgrade to more recent Closure Library and Closure Compiler. Closes #53

Upgrades:
- jsFramework 1.16.1 -> 1.17.0
- Closure library r2388 -> 99cd91

Post upgrade code fixes:
- goog.events.listen returns goog.events.Key instead of number
- goog.net.ImageLoader is final (we can not subclass it)
- goog.ui.DatePicker has better API (no need to access private members)