Delete test case stuff separately to speed up report deletion
Delete test case stuff separately to speed up report deletion

Due to :dependant => :destroy deleting really big reports is insanely
slow. Since we don't have report information on meego_measurement and
serial_measurement they cannot be deleted fast using ActiveRecord.

Decided to add functionality that will first destroy test case attachments
(because the files need to be removed from disk), then deletes the
measurements using raw SQL so they're removed quickly and finally deletes
test cases by report ID which is also really fast.

Report, report attachments, and features are removed via the dependant
chain as before because there are not that many of those.

leonidas/qa-reports,leonidas/qa-reports,leonidas/qa-reports