Settings: Build internal memory info dynamically

We can build up the extra info Preferences for internal memory
dynamically, based on how many additional volumes there actually are.
The old way was hard-coding a single additional volume in the xml for
device_info_memory, forcefully removing that when no volume is
specified for a device.  So now these internal volumes show up at the
end of the list, since they are appended dynamically, but otherwise this
should work at least as well as before, just with cleaner code.

This also converts a few setTitle and setSummary calls to use resource
identifiers directly, rather than manually calling mRes.getString.

Change-Id: I77cae0a4e29c03a0f1a3552258b634be1e9a91f7
Signed-off-by: Josh Stone <cuviper@gmail.com>