New class MinpvProcessor, and test.
Add new constructor, that can handle MINPV processing.
Documented MinpvProcessor.
Change loop order.
Remove unneeded const_cast.
Correct doc error (zcorn is also output argument).
Refactor set/getCellCorn() with private method.

Also const-ify everything that can be const.
Use syntax for std::array which works with GCC 4.4.
Merge pull request #637 from atgeirr/add-minpv

Add MINPV processing to GridManager