Add optional launcher hide/close on pack launch

This commit, coupled with its twin in the TechnicLauncher 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 #10 from Spyboticsguy/master

Add new settings option for launcher action on launch.