Explicitly create log of events related to each request

[pwalsh]

We have a number of state changes to requests that do not have data about the change persisted.

For example: change status, change assignee.

We should have a record of every change made to a request, including what the change was, and who made the change.

We can do this in a simple manner by "abusing" the RequestComment data and writing additional events. This maps well with how we display such data in the UI we have.

For these new "automated" comments we will add as records of change, we can write them to a request comment using one or several templates.

[pwalsh]

This is now implemented in #47