[#7305] Consolidate allura.model.repo into allura.model.repository

Signed-off-by: Cory Johns <cjohns@slashdotmedia.com>
[#7305] Added narrative documentation for SCM apps

Signed-off-by: Cory Johns <cjohns@slashdotmedia.com>
[#7305] fix typos
[#7305] add backwards compat repo.py back in
[#7305] add a few more repository docstrings
[#7305] bump forgehg rev for repo/repository.py merge