Issue #442 - Attempt at fixing Editing in 2.0.6

-Removed the $eval on COL_FIELD placeholder
-Simplified ng-input to only be concerned with hiding keystrokes and
using ESC to backout edit
-Use ng-model in EditableCellTemplate to do actual binding
Fixed the test scenario for editable cells.

I had to inject $sniffer and conditionally use the 'input' event in browserTrigger() rather than 'change'. Not sure why yet, but it works!
Merge branch '2.0.6' of https://github.com/angular-ui/ng-grid into 2.0.6