Add `@property-read` for group name and desc.

See #160
PHPUnit: avoid fatal error when not testing ranks

Only load the rank type mock when the rank type class is available.
PHPUnit: Don't use a deprecated method

The notices weren’t being caught before because we weren’t calling
`parent::tearDown()` in all of our `tearDown()` methods.

See #165
PHPUnit: remove bad assertion from hook Ajax test

This formerly tested the behavior of
`WordPoints_Points_Hooks::get_all()`, which is now deprecated. The
function it has been replaced with works differently.

See #165
Hook up the ranks Ajax function in PHPUnit tests

Any hooks added after the first test case has been run now need to be
added each time they are needed after calling `parent::setUp()`. This
is due to the hooks now being preserved between tests.