Log filter

- exclusion filter.
- config to control the exclusion filter.
- prefix all loggers with st2 so that the name filter always works.
The name of loggers is usually a fully qualified name like st2.st2reactor.blah. The only way I can think of improving this is by building a trie. Not sure how I would use a set and avoid the iteration.

If you have ideas please commit to the branch :)