Important improvements to the updater

[marticliment]

Reimplement the UniGetUI autoupdater from scratch.
This will allow for:

• Pre-Release/beta channel for the autoupdater
• Better communication of the update to the user
• Allow for manual update check
• Less disturbing/interrupting update processes
• More reliable version checks
• No more command-prompt jumpscares when autoupdating
• No more random crashes when autoupdating

TODO:

• Migrate VersionNumber to BuildNumber on build script, autoincrement build number

[mrixner]

Just as you've linked #1942 to manually check for UniGetUI updates, I think #2047 is relevant to this PR.

[marticliment]

Yes, it is, I didn't see the issue when looking for related issues.