Currently, removing a feed from `/category/{id}/feeds` redirects incorrectly to `/feeds`. This change fixes it so that
removing a feed will now correctly redirect to `/category/{id}/feeds`. Removing a feed from `/feeds` is unaffected and
will work as it does currently.
To fix this, a new UI endpoint `/category/{categoryID}/feed/{feedID}/remove` is added and a corresponding handler method
to validate and perform the removal from DB.
