add a hasClass() method

Two goals here:

First, the removeClass() wasn't adding spaces before and after element.className and the class. This could create weird false positives as we get into compound class names, like vjs-fluid, and vjs-fluid-4-3. This aligns the check across both methods.

Second, I think hasClass is going to be essential for testing, going forward.
Actually this should return the result of vjs.hasClass.