Migrate Squirrel to Velopack

[sshcrack]

Fixes issue #181 (maybe #192) . Migrated Squirrel to Velopack. Haven't tested updating yet and we'll have to handle Github Releases

I've made the UpdateManager a static public field in Updater to apply updates when the user clicks restart.

[sshcrack]

Alright, I'm setting up the csproj config, what should the packId be? RePlays? Also, we have to decide for a channel that velopack is going to use. I'm going for stable for now.
Folder structure looks like this:

[sshcrack]

To be done:
Github workflows.
I think a release has to be deployed manually first for velopack to create deltas and establish the update channel (and for the github workflow to work)

[sshcrack]

Sometimes delta updates are not applied when just exiting the application without calling ApplyUpdatesAndExit if an update is pending.
Maybe we could add a exit hook to the application as well to apply updates. There's more info here

[sshcrack]

@lulzsun what do you think?

[lulzsun]

I'm holding off reviewing this until I have more free time. Since it sounds like this may introduce breaking changes, I'll have to properly test this myself before making decisions.