Add setting to control the creation of NullRevision on upload
When uploading multiple file revisions with fitting text revisions to
core the UploadRevisionImporter will create a unwanted NullRevision on
the file page.
This NullRevision originates from LocalFile:upload() and is added there
in recordUpload2 as part of the normal upload process. There it is meant
to leave a hint on the text revision history.
This whole area is in need of heavy refactoring. But since the issue is
blocking the current implementation of the FileImporter extension, a
parameter is added to control the creation of that NullRevision.
Bug: T193621
Change-Id: I57c947eb63a7627ab1eec850cdf5e076f5f62df5