New daystate notificator, globalscript prefab

- Added a notification when the game switches day states.
- Added a _GlobalScripts prefab which always exists throughtout the
game. So whenever we need a script to exist at all time this is the
gameobject to put it on.
- A script called GlobalScript is attached in order to prevent multiple
_GlobalScripts objects.
- Needed this because of the level loading stuff which could not happen
from within the non monobehaviour GameManager.