Create StripeButtons class, convert reuse button to use it

Also do a bunch of refactoring to:
* keep LESS rules in more sane locations so it is not as hard to get an overview
  (most of the metadata panel rules were in mmv.less)
* move mmv.mixins.less up one directory as it is not specific to the UI
* move the SVG icons as all of them were related to the UI
* remove the marging-right hack which was used to keep the title text from
  overflowing the button; instead use a float and overflow properties to make
  sure text that is too long gets hidden

Change-Id: Icc8ea2e766be67d86ae98c734721b2185bd6c36e
Merge "Create StripeButtons class, convert reuse button to use it"