Added missing nfc_register_tag_readerwriter() and nfc_unregister_tag_readerwriter() calls

These indicate to the NFC stack what particular types of NFC tags we're interested in being notified about
and you can mix and match. The default is not to register any tag types.
Merge pull request #1 from jcmurray/master

Added missing nfc_register_tag_readerwriter() and nfc_unregister_tag_rea...