Fix minor Doxygen issues
Summary:
Minor fixes (typos, formatting, missing items).
The list of issues is from EBN:
http://ebn.kde.org/apidocs/apidox-kde-4.x/kdeutils-kgpg.html
Test Plan: Run doxywizard. Ensure that there are no warnings except for mismatched class members.
Reviewers: dakon
Reviewed By: dakon
Subscribers: kde-utils-devel
Differential Revision: https://phabricator.kde.org/D17795