The LastCommitCache code is a little complex and there is unnecessary
duplication between the gogit and nogogit variants.
This PR adds the LastCommitCache as a field to the git.Repository and
pre-creates it in the ReferencesGit helpers etc. There has been some
simplification and unification of the variant code.
Signed-off-by: Andrew Thornton <art27@cantab.net>
* Some refactors related repository model
* Move more methods out of repository
* Move repository into models/repo
* Fix test
* Fix test
* some improvements
* Remove unnecessary function
