Make the font registry cachable

Task description

If a huge amount of fonts are installed on the system, registering these fonts during the boot-up is rather slow. The booting time can be greatly increased if the font registration would be allowed to cache the font-mapping data.

Solution Approach

It is not neccessary or feasible to cache all font data. The most important meta-data that needs to be cached is the font-name and font-family data. These entries list what fonts are available and what physical font file is used when a certain logical font and style is requested by the system. The glyph-level data is not part of the cachable dataset, it can be read when the font is accessed for the first time.

The current architecture does not cleanly separate between logical and physical font data and therefore caching is not possible. Refactor that.