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.
if you make this if check !hasClass, and then return, it will keep the rest of this function not indented, which is nice.