Added exchanger methods to GroupStorage. Not tested.

Also changed multiProcDimension_ to gridFlags_ in Exchanger class.
Inlined some functions in GroupStorage.
Exchanger now uses methods in GroupStorage, tested.
Fixed bug within an assert in DdMd::AtomCollector.
Merge branch 'devel' into groups
Finished removing unused methods from Exchanger.

Removed methods had been moved to GroupStorage.