Add ability to push and pull tags
Handle tags for sparse/shallow remotes properly and report tag updates correctly in CLI.
Improved performance of LogOp when path filter is specified.

- Made the filter use FindTreeChild instead of DiffOp to specifically look for a change
at the path.
- Moved the creation of geogit commands outside of loops to avoid needless work.
Merge pull request #664 from dwins/push-and-pull-tags

Add ability to push and pull tags
Merge pull request #669 from jdgarrett/log-op-performance

Improved performance of LogOp when path filter is specified.
Add tests for new fetch behavior
Merge branch 'push-and-pull-tags'