Establish and implement UUID convention for events

Ideally we'd use such UUIDs as primary keys, but the performance of UUID
PKs in MySQL under write-heavy loads seems to be poor. But at minimum
I'd like to include them as a column, preferably with a unique
constraint.

Also bumps version to 0.5.

Change-Id: I48bc1f861cefcb8a3ff902a156b6877ad6b6e2f4
Merge "Establish and implement UUID convention for events"