Write MKV tags without mkvpropedit as a dependence for AppImages

Write the MKV's tags without mkvpropedit, e.g. with a custom writer.

Why

Calling an external program is painful. If we want to make an AppImage this is much more painful...

How

• AppImage solution: include mkvpropedit in the AppImage, with that there is no longer a dependency for the AppImage.
• The do-it-yourself solution: the tags are at the end of the file so with a truncate and simple writes it should be feasible. Here are the specifications: mkv spec. See the section Tagging at the end of the table.

Which one: the AppImage solution will be implemented first because it's the simplest one.