Ignore required fields when updating #112
Description
Right now when we update an item, we must specify the required fields. This is because we are using the same declaration for the expected fields there like the one we use for the creation.
TODO:
Search whether Flask Restplus has a way to indicate an update is being done and/or the required fields should be ignored. Otherwise, create a function in time_tracker_api/api.py, namely remove_required_constraint, which clones (immutable) the constraints of a Restplus model and return an equivalent with the fields where the constraint Required is False.