CSS Refactoring

[timlindvall]

Evaluate our current CSS and see if there's anything to clean up or refactor.

Issues rolled into this ticket

• [firefox] [css] the bubble-arrow is shifted (1px) #279 Firefox: Bubble arrow shifted 1px
• CSS Issues #276 Selectors are overly verbose. Should we use BEM instead?
• CSS Issues #276 Find a way to separate core styles from theming. (Such that core styles can be included with any theme-specific styles so it's easier to adapt the bubble theme to mesh with whichever site it's included with).
• rtl support #272 RTL support
• HopScotch arrow blocks the link or input it is pointing to. #270 Arrow is blocking interaction with element being pointed at.
• Make it easier to update look and feel using vars. (Previously reported as Provide more customizations in vars/buttons.less #99 #117)
• Choreograph an animation solution that doesn't require the JS to have any knowledge of the animation timing. (Previously discussed on Allow configurable fade duration #200)
• Don't rely on sprite for look and feel.