Previously, the Launcher was creating a new runner thread that would
call the application's main method. An exception thrown by this thread
is handled differently to one thrown by the JVM's main thread leading
to different exit behaviour. Furthermore, the separate thread isn't
actually necessary.

This commit removew the use of a separate runner thread from the
Launcher. This means that the JVM's exit behaviour will be consistent
and also removes the overhead of createing a starting an extra thread.

Closes gh-5006