WIP: move mapping from plugin to basin3d

Attempt at creating functionality to handle simple attribute mapping (e.g., statistic, result_quality) in basin3d instead of plugin

Add MappedAttribute model as a general purpose mapping object
Update catalog to handle MappedAttribute model
Add _.csv file in plugin to describe mapping [plugin redesign probably needed here]
Extracted statistic from plugin as example case -- have it working for usgs unit tests [need to confirm w/integration yet]

To Do if approach is liked:

Figure out how to handle basin3d vocabulary that is not mapped to datasource attribute
Extract ResultQuality
better type handling (have some questions here)
Documentation
Integration tests
Removed commented out code

Issue #TBD

Type of change

[x] Breaking change (fix or feature that would cause existing functionality to not work as expected)
[x] This change requires a documentation update

-- still some to dos

[ ] My code follows the agreed upon best practices
[x] I have commented my code, particularly in hard-to-understand areas
[ ] I have made corresponding changes to the documentation
[ ] My changes generate no new warnings
[x] I have added tests or modified existing tests that prove my fix is effective or that my feature works
[x] Existing unit tests pass locally with my changes
[ ] Any dependent changes have been merged and published in the appropriate modules
[ ] I have performed a self-review of my own code