Add optional launcher hide/close on pack launch

This commit, coupled with its twin in the LauncherCore repo, adds
functionality for the user to select what their launcher does upon
launching the game. It can close, hide itself until the game is closed,
or do nothing and remain open in the background.

Signed-off-by: Tristen Allen <spyboticsguy@gmail.com>
Change launcher hiding to use an Enum

Signed-off-by: Tristen Allen <spyboticsguy@gmail.com>
Merge pull request #319 from Spyboticsguy/master

Add optional launcher hide/close on pack launch