Set global state on master rank only

Set global state on master rank only

The global state class was initialized on the master rank
and broadcasted over all ranks. This lead to unnecessary communication
and it was difficult to know what part of the global state was up to
date at different points in the code.
Now only the master rank has a global state object.
This change requires conditional access to the global state pointer
for the few algorithms that use it.
Replaced bcast_state() by a function that only broadcasts x and box.
Also made the box pointer constant in domdec initialization.

Change-Id: I924487863abe096eeb0b3cbc944b4ba32898ef03