Fixed the path of the file being mixed up with the archive name.

Also removed toLowerCase() on the archive name.
Made Launcher.getInstance() create an instance of needed.
Implemented new Yggdrasil authentication scheme, but it is not in use yet.

Renamed LoginSession to LegacySession.
Changed YggdrasilSession to use HttpRequest.

Added getAccessToken() to MinecraftSession.
Merge remote-tracking branch 'sk89q/master'

Conflicts:
	src/main/java/com/sk89q/mclauncher/LaunchTask.java
	src/main/java/com/sk89q/mclauncher/session/LoginSession.java
	src/main/java/com/sk89q/mclauncher/update/VanillaUpdateCheck.java