Merge pull request #446 from andlaus/propertysystem_fixes

Property system: some simplifications and bugfixes
added: nonstandard 'RHO' field in eclipse grid parser

note that as this is a nonstandard field, there is no unit conversion
handling. use with caution
Merge pull request #447 from akva2/add_rho

added: nonstandard 'RHO' field in eclipse grid parser
unify or add the leading license comments
remove ascii art comments at the beginning of source files
add emacs and vim modelines to the C++ source files
add emacs and vim modelines to the C source files
make sure config.h is included in all source files first thing in the morning
use correct copyright attribution for the Event* files
use full copyright statement for files which mention the GPL
use the standard OPM license statement more files

(and correct the names of a few guard macros.)
remove the emacs c-basic-offset:4 local variable for emacs

these have been replaced by the modelines at the beginning of the file.