Remove ManagedRepo.createOriginalFile

Dangling methods like this exacerbate the checking
of possible synchronization issues. The one method
which should be allowed is register(); any others
should be refactored away.
Replace create() test method with RawAccessRequest

The create method was the last remnant of the previous
multiplicity of ways to create files. These have now
all been consolidated into "register()". This poses a
problem for testing though. It's no longer possible to
modify the file system without also updating the database.

In order to simulate a background user (non-OMERO) modifying
files within the repository with OMERO's awareness, the
RawAccessRequest command can be used to touch or remove files.

This can only be done by an administrator.
Add UnregisteredFileException

file() and fileById() now throw an omero.UnregisteredFileException
if a file exists on the filesystem but is not registered in the DB

The `file` field of the exception returns the OriginalFile object
which would be created if register(String path, String mimetype)
were called on the same path. If the object on disk is a directory,
mimetype must be null or "Directory".