[PATCH] [cmake] Makes arbitrary build subdirectories possible.

Instead of guessing the suffix or subdir of the build directory,
we now simply compare PROJECT_{BINARY,SOURCE]_DIR to detect it.
By this e.g. opm-core/opm-parallel is a possible build directory, too.
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
Merge pull request #113 from blattms/make-arbitrary-sibling-possible

[PATCH] [cmake] Makes arbitrary build subdirectories possible.
Added const to a couple of get-type methods
Merge pull request #120 from flikka/constify-Group-methods

Added const to a couple of get-type methods
units: substitute "FlowVolume" by "LiquidVolume" and "GasVolume"

because the units for them are different in the "Field" unit system.
units: replace "t" with "Time"

this makes things more explicit and more readable
units: Replace "L" by "Length"
units: Replace "P" by "Pressure"
units replace: "mu" by "Viscosity"
units: rename "1/Rs to "OilDissolutionFactor" and "Rs to "GasDissolutionFactor"
units: rename "K" to "Permeability"
units: rename "Rho" to "Density"
units: rename "m" to "Mass"
units: introduce a "ContextDependent" dimension

this is meant for those nasty keywords where the dimension of an entry
depends on a user-defined value of some field of a (potentially
different) keyword. One example for this are the surface rates of the
produced fluids for the .CON(INJ|PROD).* keywords which exhibit
different units depending on whether the user choses to control for
the surface gas or the liquid rate.

the approach taken in this patch is to convert all numbers to NaN if
the unit is queried in SI (via item->getSIDouble()). It might be more
desireable to throw an exception in this case, but this approach would
be more elaborate and NaNs should be quickly noticeable by the users
of this code.

I tried to adapt all implemented keywords, but it's quite likely that
I missed some...
correct the context dependent rates in the schedule code
Merge pull request #117 from andlaus/unit_system_cleanups

Unit system cleanups
Added missing files from the Utility folder to the CMakeLists file.