add the MISCIBLE keyword

it's only specified by R300, but it is required TLMIXPARAM which is used by
opm-polymer...
fix the PLYMAX keyword

- fix typo: use "POLYMER" instead of "PLOYMER"
- according to the Eclipse RM, the size of the table is given by the
  "NTMISC" item of the "MISCIBLE" keyword...
add the TLMIXPAR keyword

this is used by opm-polymer...
add table utility classes for the PLY{ADS,MAX,ROCK,VISC} and TLMIXPAR keywords

these are not really used as tables in the current opm-polymer code,
but the Eclipse RM says they are tables, so we should add these
classes...
Merge pull request #181 from andlaus/polymer_fixes

Polymer fixes