Port away from KHTML
Summary:
- use resources for included HTML files
- replace KHTML part with QTextBrowser
- open links to external websites (i.e. Wikipedia) via external web browser
- remove code for downloading and converting Wikipedia page downloads
- change all external links to https
- remove KHTML dependency
Reviewers: yurchor, vkrause
Reviewed By: yurchor, vkrause
Subscribers: vkrause, yurchor, kde-edu
Tags: KDE Edu
Maniphest Tasks: T11573
Differential Revision: https://phabricator.kde.org/D23862