Improved Solus support, and other quality of life improvments

[Batcastle]

• Fixed Solus support
• Install gnome-tweaks only if gnome-shell is installed
  • This is only added on Ubuntu as I don't know how to do this on Fedora or Solus. Someone else will need to do that work.
• Refresh repo cache before installing or updating anything, and only do it once
• Check if scripts are running as root, throw an error if not
  • Extras files where modified to handle this, and in fact require it now.
• Create unified front-end, so most users only have to run one file no matter their distro, and it handles figuring out what to do from there.