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
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
GconinjeWrapper: return raw instead of SI rates

the wrapper could be a bit more sophisticated and do the conversion
internally, but the new wells management code seems to ignore the
wrapper anyway, so there is no real point in investing time into that
(yet).
Changed the begin and end iterator functions of GroupTreeNode into const_iterators
Added test to run through the iter functionality in GroupTreeNode
Make sure that the tree is updated correctly after reading WELSPECS
Merge pull request #122 from andlaus/gconinjecte_util_return_raw_instead_of_si_rates

GconinjeWrapper: return raw instead of SI rates
Merge pull request #123 from flikka/constify-group-iterator

Changed the begin and end iterator functions of GroupTreeNode into const...
Merge pull request #124 from flikka/add-grouptree-child-iter-test

Add grouptree child iter test
Merge pull request #125 from flikka/fix-treefromschedule-bug

Fix treefromschedule bug