Add configuration options to the RSpec database query reporter

[andypike]

Allow a developer to configure what they want stats on. Currently we report the time taken and number of queries per type or class. But we are probably more interested in stats outside of feature specs and Query object specs as these are expected to have queries. Other classes under test should have less queries as we should stub out Query object usage which in turns means less setup of database state using factories. These other classes may well require database queries as they might need to confirm that database state has changed correctly for example.

[andypike]

This isn't being used by anyone and was experimental. I might remove it all together unless I hear from people that it's useful.