fix ugly bug which prevented deck keyword names from having a minus in them

i.e. MULT[XYZ]- was trimmed to MULT[XYZ]. Also, the RawKeyword now
uses ParserKeyword::isValidDeckName() instead of a regular expression
which makes it automatically consistent and also should make it
slightly faster...
GridProperty: mark getData() as const

it returns a const reference to a vector which does not allow
manipulation of its members. the getData() can thus be safely called
on constant GridProperty objects.
TransMult: implement non-fault transmissibility multipliers

i.e., the MULT[XYZ]-? keywords.
EclipseState: extend test to check the TransMult class