add proper license information to all themes
for older themes, digged out of the git history of this/ktexteditor/kate repos for newer themes just taken from the last merge requests + commits referenced license of the original authors for imported themes
add unit test that ensures all stuff is properly license
- enforce MIT as SPDX identifer
- enforce some copyright array elements are there as SPDX identifier
it is a bit 'relaxed' as we can't require contact addresses