file api: alter required fields

the file api currently requires file_type_id in the params, but as far as I can see, that field is rarely used in the normal interface upload of files.

I believe what should be required is the uri field, which is where we store the actual filename (filename as uploaded + unique hash)

see this patch (first part):
https://github.com/nysenate/Bluebird-CRM/commit/11910d3e3906d3fc16b7d4292fb52998da53a0a2