Bug 1098404 - Implement per-component filters for mozlog, r=chmanchester

This allows individual component loggers to e.g. discard all messages below a
set level, or rewrite messages from one level to another.

--HG--
extra : rebase_source : 9b37981368edb099ac555a2dacfafd486f8fcd2d
extra : histedit_source : 144d17f582944703b07529e31bf13b845d5f9695%2C706e2b7db06a1217d0e956614f0232c153a6a3d0