cache ytdl and dl audio

v3

Cache ytdl install and an option to download audio

Made the title and message of a dialog the right way around

this update does exactly what it says on the tin.

Async implemented

The app now runs async! This means that pressing the Download button will no longer cause the GUI to freeze until the downloads are finished, and instead the GUI will allow you to set up your next Download Queue and save location. Note that at the moment there isn't a queue to allow you to set up multiple different jobs to different folders in one go.

Initial Release

A Graphical Interface for the youtube-dl project.

Can download things from tons of different sites, list here.