[doc] Improves doxygen documentation of schwarz.hh.

Namely we try to document the template parameters in more detail and
make sure that cross reference to OwnerOverlapCopyCommunication,
vectors, and matrix implemetation appear.
threadsoverlappingschwartztest: created
Makefile.am modified
threadsmpitest: first commit
threadsmpitest.cc: bc added
threadsmpitest: added index set for matrix
threadsmpitest: matrix update done
simpleoverlaptest: created but schwarz operator not working as aexpected
simpleoverlaptest: not working as expected
Delete threadsoverlappingschwartztest.cc
simpleoverlaptest: fixed
threadsmpitest: cleanup of useless comments
cleanup directory
Merge branch 'threads' of https://github.com/magnese/dune-istl into threads