Release candidate: Download tab refactor

First candidate for release, should be stable regular for use.

Make an issue for feedback or if you have a problem.

• Redesigned main screen for a nicer look! Much easier too keep track of multiple downloads.
• Parallel downloads, up to 4 downloads will simultaneously download. Enable in About tab, toggle download mode to from Singular to Parallel.
• Right click a downloads filename to get the option to open folder on file. (Doesn't work for all cases, feedback appreciated)

Follow installation guidelines back on the main page: https://github.com/Thomasedv/Grabber
If you already have all the files, you only need to replace the old Grabber.exe with this new one.