Removed m_deckIndex property from DeckKeyword
DeckKeyword is immutable.
Merge pull request #381 from joakim-hove/KeywordContainer-const

Keyword container const
Make MULTREGT work for NNC.

The region multipliers are no longer added  to the cartesian logical
MULT[XYZ] structure. Instead a new method
getRegionMultiplier(globalIndex1, globalIndex2,FaceDir) is added that
return the multiplier between globalIndex1 cell and globalIndex2 cell.
The face direction is added to support directional dependent MULTREGT
input. This implementation of MULTREGT also supports restricting the
multipliers to only apply for NNC or NONNNC.
address the review comment of #373

hopefully. there was a minor problem: `deck->getKeywordList()` returns
a vector of non-const pointers which cannot be implicitly converted to
one with const pointers. I've thus adapted the type of the constructor
argument for the MULTREGTScanner...