Add polymer density unit.
Add PLMIXPAR for Todd-Longstaff mixing parameter.
Add PLYADS, dealing with polymer adsorption.
Add PLYMAX, to be used calculation of the maximum polymer fluid viscosity.
Add PLYROCK, dealing with permeability reduction.
Add PLYVISC to be used calculation of effective water viscosity.
Add PLYSHEAR, to be used calculation of shear thinning/thickening.
ScheduleEnums: strip whitespace around the control mode strings

for some reason, the Norne deck included whitespace for some control
modes of some wells which lead to an exception. Since Eclipse seems to
eat this, and Eclipse is correct by defintion, let's adapt our
digestion system a bit...
Merge pull request #145 from andlaus/ScheduleEnums_strip_whitespace

ScheduleEnums: strip whitespace around the control mode strings
Add PolymerDensity to system.
Merge pull request #144 from qilicun/polymer_units

Add polymer density unit.
Merge pull request #147 from qilicun/polymer_keyword

Polymer keywords
Minor syntax fix in JSON config.
Merge pull request #148 from joakim-hove/polymer-fix

Minor syntax fix in JSON config.
Added method at() to the dynamicstate object to return a const reference.