Support Polymer v1.7.0

• Fixes:
  • Use latest release of Hydrolysis. Polymer Analyser is not an option because it does not give type info yet.
  • Make DOMTokenList mutable
  • Avoid overriding methods with the same signature and different parameter names
  • Generate correctly EventHandlers for widgets
  • Compute correctly bower dir location
  • Set correctly arrays and objects values in UiBinder attributes.
• Breaking changes:
  • Depend on GWT 2.8.0 final. -XjsInteropMode is not needed anymore
• Features:
  • Load webcomponents.js polyfill if needed, skipping browsers with native support.
  • Better handling of imports, so as we only load once and only if not done already in the host page (allows vulcanize)
  • Add UiBinder String setters for all properties in widgets.
  • Remove unnecessary Bower files during package phase
  • Add Polymer.dom API