IE8 Fixes (part 2)

Three small fixes here:

* #434 - CSS tweaks: Adding fallback colors for `rgba`, and swapping `::after` for `:after`
* #435 - Enable CORS support in jQuery
* #430 - Click event handler changes
@krues8dr just to clarify what you mean by working, do you mean that the tests are passing with this change? Or that all aspects of the reading/writing/editing/deleting annotations work when running annotator in IE8 with this patch?