Changed name of items in PVCDO keyword.
Merge pull request #225 from joakim-hove/fix-PVCDO

Changed name of items in PVCDO keyword.
Added Box() class to book keep the indices in a box.
Added constructor for sub box.
Added Box::equal() comparison function.
Added BoxManager() to keep track of the currently active input box.
ERT-656: Changed GridProperty to take (nx,ny,nz) instead of volume.
Basic BOX support when reading integer properties.
Added iterators begin() and end() to DeckKeyword class.
Added copyFrom() property to GridProperty
EclipseState now handles COPY keyword.
Added support for MULTIPLY keyword.
Added new keyword PVTNUM
Supporting the ADD and EQUALS keywords.