Resolve "Create separate class to read list of fires from config, fetch data, and add updated data to data store"

Closes #23 (closed)

• refactor datastore and mesowest modules to be more self-contained
• update mesowest to no longer batch station data requests (batch by fire)
• move fire update logic to separate module under cli
• add test fixture mock_datastore for testing
• use requests_mock for requests mocking
• update api docs

/cc @hschovanec