[2padaptive] Fix pressure reconstruction for 2p adaptionhelper

Merged Martin Schneider requested to merge fix/adaptivity into master

For some grids, e.g. UGGrid, the father element is identical to the son element. It is therefore not a good idea to use the adaptedValue containers for the father and for the son element since they might be also identical. This has been changes such that the adaptedValues are no longer modified in the reconstruction routine.

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