Added a function to translate trigger candidate type to string

[bieryAtFnal]

Also, added a TriggerCandidateData unit test to validate the translations to/from TC types and strings.

This change was made as part of providing the ability to apply different acceptance criteria for different trigger types in automated integration tests (i.e. the integrationtest package data_file_checks).

The simplest way to test these changes is to run the new unit test...

• create a software area based on a recent nightly build
• add this repo to that software area and check out the kbiery/get_tc_type_names branch; rebuild the software
• dbt-build --unittest trgdataformats
• dbt-unittest-summary.sh

[aeoranday]

LGTM.