Added migrations for gdb_pe robot cert and 'background' tag. Also added 'background' to the list of blessed tags in the settings module.

The IVORN must have a hash sign between the fixed part (the 'ivo' bit) and the event-specific part (the 'resource number', or in our case, the graceid).

Made changes to bring VOEvent closer in-line with what Mina and Peter are proposing. However, I still don't have their AlertVersion property. Nor do I have any of the analysis specific stuff, like ChripMass, frequency, etc.

Conflicts:

	settings/default.py