Store the Github event in the events table

This patch simply stores the Github payload and request into the events
table.  All events have the same name, which is perhaps a really bad
idea.

Limit the number of saved events to the most recent 100

Without this patch the application will persist requests without bound.
This is a problem because we don't want to worry about maintaining this
application over time.  This patch addresses the problem by limiting the
number of events that we persist to the 100 most recently received events
by default.