gplugin/gplugin

Add a doc check unit test to gplugin-gtk and fix the issues it found

Testing Done:
Ran the unit tests

Reviewed at https://reviews.imfreedom.org/r/3040/
<?xml version="1.0" encoding="UTF-8"?>
<gresources>
<gresource prefix="/org/imfreedom/keep/gplugin/gplugin-gtk/">
<file compressed="true" preprocess="xml-stripblanks">plugin-page.ui</file>
<file compressed="true" preprocess="xml-stripblanks">plugin-row.ui</file>
<file compressed="true" preprocess="xml-stripblanks">plugin-settings-list.ui</file>
<file compressed="true" preprocess="xml-stripblanks">view.ui</file>
</gresource>
</gresources>