GET /inputmasks/{idxes} can hang "forever"

[sbellem]

Problem: The current backend logic is such that if a client requests an inputmask that cannot be found in the db, the backend will wait and until it can be found. In the meantime the request never returns.

Proposed solution: Try to access the requested inputmask just once, and if not found return a 404 not found error, and leave it up to the client to retry.