Graphics.Input.focusables implementation similar to hoverables
Graphics.Element.focused to demand focus after next render.
Change semantics of keepWhen/dropWhen.

They no longer propagate the right Signal when the left Signal
changes.
Uncomplicate keepWhen implementation
Remove old JS dropWhen/keepWhen
corrected documentation of keepIf and friends
Add The ability to track and set the focus of various Elements
Merge branch 'dev' of https://github.com/sgraf812/Elm into devier

Conflicts:
	libraries/Native/Graphics/Input.js
Merge branch 'keepWhen' of https://github.com/maxsnew/Elm into devier
Use maxnew's native Trampoline support for unbounded recursion

Conflicts:
	libraries/Native/Trampoline.js
Fix typos in the native Trampoline implementation and switch Right and Left
Add focused and focusables to docs.  Allow for unfocusing Elements.