Fix PHPDoc and typos

Some things my IDE complained about while creating a custom backend.

Fix PHPDoc and typos

Some things my IDE complained about while creating a custom backend.
Merge remote-tracking branch 'origin/fix-phpdocs-group' into phpdoc-improvements

Conflicts:
	lib/private/group/database.php
	lib/private/group/dummy.php
	lib/private/group/example.php