augmented autotooltips plugin: don't override any existing tooltip on a cell (modern slickgrid formatters can add their own tooltips to cells by augmenting the cellMetaInfo.attributes array or cellMetaInfo.toolTip member
cellRangeDecorator: switching to using CSS box-sizing:border-box to simplify the rendering of the overlay; this also serves as a simple test for switching slickgrid over to border-box modeling (that way it's easier to dynamically modify slickgrid cells without the need to have JavaScript code recalculate the width/height, i.e. DOM+CSS only editing suffices.
cellSelectionModel: accept NULL ranges (backpatching a fix from our app code)
drawRowManager: be more specific in accepting/ignoring draginit events: only 'accept' them as being ours when we're on top of a 'dragrow' because anywhere else doesn't matter, not for the rowDragManager anyway.
(Same check as already present in dragstart)
- Revert event handling logic in Slick.EventData and make the new behaviour optional: by default, EventData does *not* pass preventDefault, stopPropagation and stopImmediatePropagation signals to the originating event, if any.
  This fixes problems with combining multiple drag-hooking plugins in a single app.

- Add Slick.HtmlEntities class to help encode input for adding into DOM node attributes and or DOM text elements
- all formatter runs now include appendMetadataAttributes() to render the possibly complex cell DOM tweaks rendered by the formatter at hand: it may edit the cell DIV's CSS class list, CSS styles and/or other DOM node attributes. Now all formatter runs go through (almost) the same hoops and offer (almost) the same level of sophistication in rendering both grid and header cells.

- JSHint /JSCS happiness

- added preliminary feature where DOM nodes are delayed in deletion. Just a performance experiment going on...
- BREAKING CHANGE: previous commit changed the interface to asyncPostRender: adapted the examples and tests which are impacted by this change.

- `grunt less` run.