Window resize timeout to prevent poor resize performance on IE

IE triggers many resize events when resizing a window.  This causes many RebuildGrid calls to execute - leading to poor performance (especially if the grid viewport has many rows).

I've used the angular timeout wrapper to prevent multiple unnecessary calls to RebuildGrid.  This should alleviate the performance issue on IE.

Have a look at this commit: https://github.com/junketjim/ng-grid/commit/7e89ba11d1fced60ebedd09c636cf27f9bb0a5c2