Use std::bitset<dim> instead of Dune::FieldVector<ctype,dim> for the shift

The shift of a YGrid is used to differentiate element Ygrids from vertices
Ygrids etc. However, their values are only a combination of 0 and 0.5 .
The same behaviour can be achieved by using a bitset and hardcoding the shift 0.5
if an entry is true.
Additionally, the shift isnt really needed in the sizeArray helper function
and is thus removed.
Communicate the minimum amount of data necessary

Until now, the mpifriendly_ygrid hasnt been touched. Reevaluating
the minimum amount of data needed in communication lead to size and
origin of the ygrid, nothing else. The shift was communicated for
checks before, but as a user wouldnt/shouldnt touch this at all, it
is unnecessary.