Adding logic to delete environments to rest api and ui

[costrouc]

Closes #124

Adding the ability to entirely delete an environment

[costrouc]

Currently getting a few errors on not clean sqlalchemy deletion. Need to investigate further.

conda-store-worker_1  | sqlalchemy.exc.IntegrityError: (raised as a result of Query-invoked autoflush; consider using a session.no_autoflush block if this flush is occurring prematurely)
conda-store-worker_1  | (psycopg2.errors.ForeignKeyViolation) update or delete on table "build" violates foreign key constraint "environment_current_build_id_fkey" on table "environment"
conda-store-worker_1  | DETAIL:  Key (id)=(4) is still referenced from table "environment".
conda-store-worker_1  | 

And several other similar errors I'm seeing

[costrouc]

Sometimes it eventually works for deletion. This still needs to be fixed.

[costrouc]

Not too confident on post_update=True but for now this works. Looks to be fixed.