Add option to exclude tickets that were closed with little or no effort

There are a few scenarios where a ticket gets closed with little or no effort. Examples include:
* Tickets closed as duplicates
* "wont fix" tickets
* Tickets that were accidentally fixed elsewhere
* Tickets that are no longer relevant for whatever reason
* Tickets that have no time logged against them

We should add an option to _exclude_ these tickets when evaluating past performance (velocity, ticket close rate, etc).

The assumption here would be that the ticket being inquired about (the target ticket) _and all tickets ahead of it in priority order_ do _not_ fall into this little/no effort category, so there is no value in including such tickets for forecasting. Including them would give us an artificially high forecast.