Support normalized case for study names

[jimmymathews]

For better flexibility on the frontend side, let's make the API handlers support lower-cased normalized versions of the study names throughout. This is probably as simple as updating the _retrieve_study_database method to look for a match rather than an exact match (as is done now).

[jimmymathews]

This will also fix the errors associated with the occasional unexplained lowercasing. As seen by the API server recently, e.g.:

ValueError: Study name invalid: "head and neck mpif ..."