Add the field mirror_path to RepositoryResource.

This adds the mirror_path field to RepositoryResource. This field
was previously not exposed in the API.

Reviewed at https://reviews.reviewboard.org/r/4897/
Fix a stray comma in RepositoryResource.

This comma was accidentally introduced in a recent change to
RepositoryResource, and broke things. It's now removed.
Fix displaying review requests for a group on a Local Site.

The page showing review requests for a group wasn't passing in the
Local Site, due to a recent change. This meant that those using Local
Sites would get a blank list of review requests when viewing a group.
Merge branch 'release-1.7.x'
Release Review Board 2.0 beta 1.
Bump to 2.0 beta 2 dev.
Handle unicode/str cast operators.

A few of our objects defined __str__ and/or __unicode__ methods. This presents
some complications for porting to python 3, since str has different meanings.

Django provides a decorator, @python_2_unicode_compatible, whereby you define
__str__ using python 3 semantics (i.e. it returns unicode), and when running
with python 2, it will rename that to __unicode__ and make __str__ call that
and encode to utf-8.

Testing done:
* Ran unit tests
* Checked list displays in the admin

Reviewed at https://reviews.reviewboard.org/r/4920/