Port to Plasma 6

[RiskoZoSlovenska]

This PR updates the plugin to Plasma 6 and cleans up the CMake and README files a bit.

Notable side effects:

• Support for Plasma 5 has been removed. As there are people still using Plasma 5, I recommend merging this PR into a new branch instead of master (or archiving the current master into a new branch).
• The plugin ID, and thus the configuration group name, has changed from Translator to krunner_translator; users who upgraded from Plasma 5 will need to reconfigure the plugin.
• The installation instructions have been updated; the README lists the commands to run and the installation/uninstallation scripts have been removed. This is a somewhat opinionated change, as I believe the scripts did not offer much value and I'd prefer users read the commands they run on their machine.
• The uninstallation scripts now attempt to install the required build and runtime dependencies (including translate-shell) via apt or dnf.
• The README no longer lists dependencies for OpenSUSE.

Closes #30.

[thegrasshopper104]

I tried simply installing your version from the store but it fails:

/home/aronkvh/.local/share/krunner-sources/krunner-translator-1.5.0/install.sh
/home/aronkvh/.local/share/krunner-sources/krunner-translator-1.5.0/install.sh: sor: 8: kf5-config: not found
/home/aronkvh/.local/share/krunner-sources/krunner-translator-1.5.0/install.sh: sor: 8: kf5-config:  not found
/home/aronkvh/.local/share/krunner-sources/krunner-translator-1.5.0/install.sh: sor: 8: cmake:  not found

Building from your fork worked luckily, and (except for TTS) it works for me.
Thanks for the port :)

[RiskoZoSlovenska]

Hi @thegrasshopper104, I haven't published my fork to the KDE store; you tried to install the original version. I forgot to remove the store link from my repo and will do so now.

The plugin uses translate-shell for TTS, which in turn needs mpv, mplayer or mpg123. Make sure you have one of those installed. Thanks for your feedback!