connect_and_remove_transfer_files: delete full transfer from ES

Previously, this function queried the database for a list of files in
the transfer, and removed those specifically. However, since the
search index contains many files that aren't in the database (such
as logs and metadata files), this left dangling files that could
never be removed.

Instead query the database for transfers, then delete all files in ES
from each of those transfers.

refs #7357
use generic version of elasticSearch remove files method

refs #7357

When deleting files from the ElasticSearch index, take
advantage of the change in commit c0eb597c630a482ffcb8b2056b04f3f605265114
that provides a more generic remove method.
Dashboard API: PEP8 cleanup
Dashboard: Cleanup helper functions

Remove duplicate definition of transfer type directories and move to where
it is called. Only called one place, and unlikely to be used elsewhere, so
shouldn't be in helpers.
Dashboard API: Clean up HTTP responses
Dashboard API: Endpoint for all waiting units

refs #7374

Add an endpoint that returns every unit that is waiting for user input,
including the name of the microservice it is waiting at.