fix(cellNav): Minor fixes and speed improvement
fix(gridUtil): Allow multiple logDebug params

The function was previously only allowing one parameter. Now the args just
get passed straight on to $log.debug
fix(GridRenderContainer): Correct prevScroll*

prevScrollLeft and prevScrollTop were being set improperly in the
adjustScroll* methods. Neither were accounting for the viewport, causing
the value to be too large. Now it only sets the value if the scrollLeft or
scrollTop argument is not provided, and it includes the viewport in the
calculation.

Also minor fixes within cellNav
fix(Filter): Watch running w/o change check

The filter term watches were all firing whether or not there was a change
to the values!
fix(uiGridMenu): Only run applyHide when not shown

applyHide() was running on all GRID_SCROLL events, whether or not the menu
was visible. This was causing excess $digest() loops.
fix(Grid): Avoid too-early header height calc

renderContainers with no canvasWidth were having their heights calculated.
If their columns were wrapping around it would mean too large of a height
on that renderContainer, and thus would be propogated to ALL the other
containers (i.e. pinned containers).
fix(cellNav): Don't lose focus with wrapping nav

When navigating beyond the left/right edges of grid around to the other
side, the grid was losing focus which prevented further navigation because
any keydown events were being sent to <body> (the new activeElement). This
fix causes the renderContainer to be REFOCUSED after a GRID_SCROLL event
in the case that the activeElement is document.body. We are assuming that
when scrolling within the grid, an element within the grid should have
focus.
fix(Edit): Retain "focus" in endEdit()

When hitting the ESC key in a cell while editing it, the cell was losing
focus when it should have been retained. This fix accounts for the changes
to using actual CSS classes instead of relying on :focus.
Merge pull request #2084 from angular-ui/cellnav-and-speed-improvements

Cellnav rewrite and speed improvements