update keyword PLYADS.
Changed order of dimensions in PLYVISC
update PLYADS "dimension".
Merge pull request #309 from qilicun/plykw

update keyword PLYADS.
add most of the keywords required to parse decks used by the IRIS history matching codes

this basically comes down to adding a few flag keywords but also
requires to add a few E300 fields to TABDIMS...

the grid cannot be instantiated yet as these deck seem to use some
peculiar constructs to specify the grid data. In particular it uses
property modifiers for keywords that specify the grid. (which might be
not allowed by Eclipse but work anyway...) the deck contains something
like

```
GRID

EQUALS
DX  50.0 /
DY  50.0 /
DZ  50.0 /
/
```

which Opm::EclipseGrid can't handle yet because grid properties are only
evaluated after the grid has been instantiated...
Merge pull request #313 from andlaus/add_more_keywords

add most of the keywords required to parse decks used by the IRIS history matching codes
New MULTREGT test based on copy FLUXNUM -> MULTNUM
Merge pull request #315 from joakim-hove/MULTREGT-MULTNUM

New MULTREGT test based on copy FLUXNUM -> MULTNUM
Added iset() method to GridProperty
Added GridProperty::multiplyWith( )
Added containsNaN() method to GridProperty
Added keyword MULTPV
Added post processor to GridProperty
Added postprocessor properties to scatter from top.

For the petrophysical properties PERM? and PORO only the top layer must
be specified, cells further down can be copied from the layer
above. This functionality is implemented with a GridProperty
postprocessor.
Added functionality to calculate PORV property.