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