With this patch, Entity::father, Entity::subEntity,
IntersectionIteratorWrapper::inside and IntersectionIteratorWrapper::outside
return entities instead of entity pointers.

Warning: This will definitely break compatibility with the 2.3 release.

the problem was that the search for the periodic neighbour deletes the periodic
boundary faces from the boundary and the elements get oriented between insertion
and this. So it does not find the elements. Now the search is done after the recreation of
the boundaryIds with respect to the new element orientation

GCC with -Wall will warn about the latter.

For std::conditional

in the case of ALBERTA-refinement it is necessary to communicate
3 levels of refinement per face, as a single element refinement
may induce a triple refinement of a face.

it now exploits the fact, that refinement calls are boolean
due to the recursive nature neighbours may be assigned at the wrong time
which in parallel leads to wrong face refinements.
this is caught by returning false and the refinement is
initiated again.