Redmine uses journals to track changes to Issues. Whilst theoretically a
polymorphic association, there are a bunch of places where it is assumed
this is an issue, so we have to account for that and start patching
things.
Refs #3320
Add a TimeBudget model which allows a job to have a time budget for each
activity type. We’re allowing nil as a holder for a generic budget,
though there’s currently no way to use that.
We automatically delete any time budgets which are set to zero.