Create Default Bag Indexes when addFsToIndexes is called but no index has been defined for that type

The basic idea is that CAS.addFsToIndexes(FS) and
IndexRepository.addFs(FS) should always add the FS to an index. If
no appropriate index occurs we just create a bag index. The FS can be
retrieved by using IndexRepository.getAllIndexedFS(Type).

The thinking is that if an annotator bothered to try to add something
to the indexes, there was a reason for it, and it's a whole lot better
to respect that than to just silently ignore it.

Note that this doesn't cause any loss in performance if an annotator
never adds an FS to the indexes. We still support subordinate FS that
are linked off of other FS but never indexed.

More discussion here: http://www.mail-archive.com/uima-dev@incubator.apache.org/msg01132.html