Author field does nothing when trying to filter a SCMSource repo

The functionality of filtering by author/committer does not work when applying it to a SCMSource based repo.

The causes are:

• SCMSource repos do not use Lucene so have no explicit committer mappings
• SCMSource always returns empty lists for the findAuthors() method so you cannot retrieve authors for the repo
• CommitterUserMappingManagerImpl.getImplicitCommittersForUserInRep() requires the repos it searches to accessible via RepositoryHandler objects (which the repositoryManager can return) but SCMSource repos cannot be accessed that way

Perhaps a simple solution would be to disable the Author field in the changeset filtering panel (insertConstraintsForm.tag) if the repo selected is a SCMSource type.