Fix appstream metadata filename and some content, and install it
Summary:
- metadata files for addons should have name %{id}.metainfo.xml
- <extends> id was not matching the kdevelop one
- <name> should be a human-readable normal nam
- add links to bug tracker, help, donation
Reviewers: brauch, apol
Reviewed By: brauch
Subscribers: kdevelop-devel
Differential Revision: https://phabricator.kde.org/D9488