PlyadsTable: do not require the second column to be strictly monotonic

monotonic is sufficient. thanks to [at] qilicun for the catch!
PlyadsTable: add a unit test and fix a copy-and-paste bug unearthed by it
remove dangling file opm/parser/eclipse/Utility/tests/TableTests.cpp

somehow this fell through the cracks when doing the big tables overhaul.
remove the TlmixparTable class

that's because the TLMIXPAR keyword is not a table...
Merge pull request #322 from andlaus/non-strictly_monotonic_in_plyads

PlyadsTable: do not require the second column to be strictly monotonic