Added getNodes to get a vector of the group nodes in the tree
Added isProducerGroup to Group class, need this in opm-core
Added setting of the injection/production status of group
Added missing files from the Utility folder to the CMakeLists file.
Merge pull request #121 from flikka/fix-cmakefilelist

Added missing files from the Utility folder to the CMakeLists file.
Merged from upstream/master
Merge pull request #118 from flikka/getnodes-grouptree

Added getNodes to get a vector of the group nodes in the tree
Merge pull request #119 from flikka/add-producergroup-status

Add producergroup status to Group object