Verify mimetypes for all existing sample files, add some more

Summary:
Check if the mimetypes for the existing mimetypes can be
determined correctly.
Also add some samples which triggered false matches previously.

Depends on D20045

Test Plan: ctest

Reviewers: Baloo, Frameworks, astippich, ngraham, poboiko

Reviewed By: Baloo, astippich, ngraham

Subscribers: kde-frameworks-devel

Tags: Frameworks, Baloo

Differential Revision: https://phabricator.kde.org/D20046