APT shared font loading

Adds support for the APT service GetSharedFont function. The "shared font" is a system-wide font that is encrypted and compressed within the system NAND (see http://3dbrew.org/wiki/Title_list). The format of this font is BCFNT. Retail games and system titles require this font to render text, and typically check that it is valid at startup. As such, having a valid shared font is typically necessary to get past initialization of these applications. 

Fortunately, this can be dumped quite easily from RAM using a simple homebrew application and the ninjhax exploit. I'm going to add this homebrew app to our org in a followup PR, as well as documentation on the wiki.
Not very, since our HLE code doesn't care about it and any client code is unlikely to check this field. That said it's better to have it because otherwise it'll generate a lot of work when we switch to something more closely mimicking the 3DS.