generate reduced remixicon sprite

[fthobe]

Desired Behavior
The Remixicon sprite is very heavy, 700KB for the currently used version, 1.5Mb for the current updated remixicon sprite. Compression reduces the size to ~150kb, which is still a lot of excess weight. I think we can do better, we should build the sprite by our own for frontend and backend as we do not need hundreds of KBs to be loaded.
svg_sprite from fnando could be an alternative.

A solution could also be to separate backend and frontend sprites.

[fthobe]

this would introduce some significant changes as I introduce a new gem into the requirements and we would also have to document everything.

This makes from an SEO, hosting cost and technical perspective absolutely sense, does it have any chance to be merged?