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
Added new DeckFloatItem with tests
Added DOUBLE enum to ParserValueTypeEnum
Renamed FLOAT to DOUBLE in JSON files, tests and some code using the enum
Added ParserFloatItem + some tests. More tests may be needed.
Removed special float/double handling in ParserFloatItem
Merge pull request #126 from AtleH/floatitem

Added DeckFloatItem, ParserFloatItem