Allow installs and removals to be cancelled

[HebaruSan]

Problem

The GUI progress screen has a Cancel button, but it only works while a download is in progress. If you try to cancel after the downloads are finished but installation is still in progress, the button disables itself and nothing else happens.

Cause

The downloaders have their own custom CancelDownload methods, but the ModuleInstaller has nothing equivalent.

Changes

• Now the downloader classes are refactored to accept CancellationTokens in their constructors and throw CancelledActionKraken in place of their proprietary APIs. The CancelledActionKraken causes the installation transaction to abort, which restores the original state of the game folder.
• ModuleInstaller is updated to work the same way and checks the token in between installing or removing files
• The Cancel button now cancels the current CancellationToken

This allows the Cancel button to work regardless of which step is currently in progress.