Merge request - add functions for looking up file records - topic/seth/add-file-lookup-functions

It was pointed out on the mailing list by Jereme Lamps that functionality for looking up file records by their IDs was not supported. This branch (topic/seth/add-file-lookup-functions) adds support for this with the following two functions:

Files::file_exists(fuid: string): bool
Files::lookup_File(fuid: string): fa_file