cleanup: Move Demultiplexer.java to different package.
front: Remove zipped-rom feature for now.

We'll probably do it differently once the carousel is finished. e.g.
user touches 'refresh' and then the app scans for .z64, .v64, .n64, and
(optionally) .zip files. If it finds zips with roms in them, it unpacks
them once to a stable (non-tempor​ary) location.  No repeated unpacking
all the time.
front: Add ROM header data to UserPrefs as a convenience.
front: Vastly simplify the crc lookup for building the cheats menu.

At least on my Nexus 7, the expensive part is parsing the cheats data
and building the cheats menu, not computing the crc.