kcms/soundtheme: Sound theme installation from file

Reason for the change

Previously, there was no way to install sound themes other than manually extracting and moving the theme folders into .../share/sounds. With this feature, users can install downloaded sound themes using a button (or dragging the theme onto the kcm) which handles the installation for them (similar to other kcms).

Test plan

I tested this with different archives (.tar.gz, .tar.xz, .tar.bz2, .tar.lz, .zip) and also different internal structures, i.e. some were tar bombs, some had many nested directories in them etc. I also tested them with invalid themes, which should result in an error message that the theme was not installed.

Screenshots or screen recordings

Before	After