Initial commit of SplitView

Functionality implemented:
  - layout of pane and content for overlay and inline display modes
  - events (beforeshow, aftershow, beforehide, afterhide)
  - animations (showPane, hidePane)
  - An equivalent of _Base._lazy for SplitView which is implemented in
    TypeScript. A non-toplevel require is used in place of _Base._lazy.
  - Unit tests for SplitView initialization, property manipulation,
    events, and animations.

Other changes:
  - amd.js: Added support for non-toplevel requires
  - _TransitionAnimation.js: Extended fast animations API so that we can
    have slow animations for debugging and non-PVL animations can adjust
    their timing accordingly.
  - Animation.js: Added a private resize animation.
  - Added require.d.ts for require.js so that we can do requires (not to
    be confused with import-requires) in TypeScript.
  - Added SplitView to winjs.d.ts.