Exclude terms

Closes #1616 - precursor to #1527 

Adds *exclude* and *include* params to the *terms* agg builder

- Add `regex` agg type
  - Add `regular expression` editor
  - Add `RegexAggParam` class
- Change how AggParam classes are loaded (based on type)
  - Updated tests
- Added `label` filter with tests

The label filter was added so I could use the aggParam name as the field label - that filter may be useful elsewhere, and could probably use some extending.