Fix error if no NATS and NATS text changed

See http://forums.musicbrainz.org/viewtopic.php?pid=25362 for reported
error.

If VA or NATS name is blank, reset to default.

If tagger.nats not initialised, don't call update.
Add NEWS
Address Bitmap code style comment
Address bitmap comments
Use dict not list to refer by name not index
Revert "Use dict not list to refer by name not index"

This reverts commit bbebb12baaf57810321d8f73a0578d7c05ce13ed.
Revised way of referring options by name