Remove "Review groups cannot be created or modified through the API." text.

When we added the ability to create or modify review groups through the API, we
neglected to remove the text that said you couldn't do it. This was highly
embarassing and probably contributed to many of the questions we've received
over the past year or so. Trivial change.
Merge branch 'release-1.7.x'
Add a basic OS X Server installation doc.

This doc mostly just links over to the Linux instructions, but it includes an
OS X-specific command for configuring memcached start-up.

Testing done:
Built manual and checked that the new doc looked correct and all the links worked.

Fixes bug 1758.
Remove woefully inadequate query parameter preservation in datagrids.

We had code to preserve some of the query parameters across pagination links
for the datagrids, but it was very inadequate. I've done a much better
implementation in djblets, which means that this can go away.

Reviewed at https://reviews.reviewboard.org/r/5355/
Add protection classes to PHP function regex.

If people are using 'public', 'private', or 'protected' on their PHP function
names, our interesting lines regex wouldn't find them. This change adds them to
the regex and includes a test.

Testing done: Ran unit tests.

Fixes bug 2951.

Reviewed at https://reviews.reviewboard.org/r/5359/
Allow people to hide repositories which no longer exist.

The repository form validation always checked that the repository existed, but
this neglected the case where someone had decomissioned an old repository but
wanted to keep the review comments around.

This change makes it so people can hide repositories even if they no longer
exist.

Testing done:
Took a repository that wasn't accessible (my local p4 without p4d running) and
tried to save it. Saw that it failed. Un-checked "Visible" and saved
sucessfully.

Fixes bug 2361.

Reviewed at https://reviews.reviewboard.org/r/5360/
Use call_command to invoke loaddata.

When triggering loaddata from rb-site, we were using an old method of invoking
the command which wouldn't set up default values for options. This change
updates us to use `call_command()` instead of `handle()`

Testing done:
Smoke tested rb-site install.

Fixes bug 3126.

Reviewed at https://reviews.reviewboard.org/r/5356/
Merge branch 'release-1.7.x'
Add support and docs for adding columns to datagrids.

This brings over the new DataGridColumnsHook into the
reviewboard.extensions.hooks namespace, and introduces a specialization
for the dashboard called DashboardColumnsHook.

There's also docs covering how to use these new hooks, along with
examples.
Clarify DashboardColumnsHook behavior in DataGridColumnsHook docs.

This makes it more clear that columns added using DashboardColumnsHook
will only be added to the dashboard's datagrid, and not any others.