Disk space check

[Tostifrosti]

The launcher needs to check if there is enough disk space, before downloading the game files (first install or update).

Instructions:

• Download 'instructions.json'
• Check how many bytes needs to be downloaded
• Check how many disk space is available.
• Optional: Give feedback to user

[JAJames]

I like the idea, but it may be best to keep this to the initial installation. Otherwise if we want to prompt users before downloading, then downloading will have to be delayed to post-verification, which could lead to a very odd user experience and would increase the total time to patch.

[JAJames]

That said sanity checks while updating could also be useful, just as an error prompt rather than "are you sure?" type of prompt