main/postmarketos-ui-plasma-bigscreen: new aport

There we go, literally months of work went into this but I think it's ready to be reviewed and hopefully merged!

This is Plasma Bigscreen, an interface from the KDE community made for TVs ("10-feet UIs"). Maybe at some point we can run postmarketOS on actual TVs, but till that happens we can at least run it on setupboxes, RPi's and RockPro64's 😄

This makes use of MyCroft, an open-source voice assistent. Note for the privacy conscious: by default it connects to https://home.mycroft.ai for configuration and routes voice commands through the MyCroft servers to Google to determine what is being said. However, you can configure it to connect to a locally hosted version of both these things. Note that the MyCroft servers are a proxy between you and Google, so Google never knows where the command came from or who said it. If you still don't want your voice send to Google, you can configure other STT engines yourself, there are multiple options available.

By default some MyCroft skills are pre-installed (just the basics to get it running), but more are available from the Alpine repos named as mycroft-skill-<name of the skill>, e.g. mycroft-skill-pokemon. For convenience a meta packaged mycroft-skills is available to install most of them.

And if you don't want MyCroft at all, just deinstall plasma-mycroft and mycroft-core and it'll run without it!