parameter system: fix problem where template brackets can be mistaken as operators

this problem occured if the GET_PARAM macro was used within
OPM_THROW. I'm not really sure whether this is a compiler bug or if it
was a bug in the code...
eliminate exceptions.hh

this gets replaced by opm-core's Exceptions.hpp and
ErrorMacros.hpp. Also, this commit replaces most instances of
DUNE_THROW by OPM_THROW. (exept in the fork of dune-istl's linear
solvers.)