basic functionality for saving registration records.  However, no migration file--need to decide whether this will wait for develop branch (2 months), or if there's another way to approach.

Conflicts:
	kalite/securesync/devices/api_views.py
adding migration file
cleaning up logic for exceptional case--where RDPK is used, but no Device object exists (must have been deleted / failed to have saved
renaming variable based on code review
Merge pull request #658 from bcipolli/save_registration_stats_develop

Save registration information