Push Tag/NdefTag implementation details into the service.

Tag/NdefTag objects should just be simple data objects. Push the mapping of
internal tag type to public rawTarget/ndefTarget into Nfc Service.

This gives an oppurtunity to clean up some Tag/NdefTag API methods. Most
significantly, adding createMockTag() and createMockNdefTag() to help with
application testing.

There will probably be some more tweaking of the types/targets in
Tag/NdefTag to come, this commit makes that a lot easier.

Also:
- Introduce getActivationBytes() and getPollBytes(). These are just stubs
for NFC service to implement, we have feedback these are really important
to help identify NFC tags.
- Based on outside advice, remove 3B_PRIME (roll into 3B) and TOPAZ (roll
into 3A).

Change-Id: I3e6789c047f6ee5c298bf76c65e0885cf3c15d97
Signed-off-by: Nick Pelly <npelly@google.com>