Added a button to the offline name selection dialog that allows
switching the intent from offline launch to online launch.
This lets you launch online with a currently offline account when you regain
network connectivity.
The servers are no longer there and there is no point keeping dead code around.
This also means that we are entirely dropping support for macOS older than 10.13
because older versions don't work with MSA.
Any remaining Mojang accounts will be silently removed.
Doing the whole 'secrets' thing by trying to hide MSA client ID was honestly crazy.
To everyone who tried to work on the code and couldn't use their own development build, I am sorry.
This makes the account system much more modular
and makes it treat errors as something recoverable,
unless they come directly from the MSA refresh token
becoming invalid.
