add flow_ebos, an ebos based simulator

it uses ebos for linearization of the mass balance equations and the
current flow code from opm-simulators for all the rest. currently, the
results match the ones from plain `flow` for SPE1, SPE9 and Norne, but
performance is not optimal: on SPE9, converting from and to the legacy
data structures takes about a third of the time to do the actual mass
balance assembly. nevertheless `flow_ebos` is almost as fast as plain
`flow` for SPE9. (for Norne `flow_ebos` is about 15% slower, even
though the results match quite closely. the reason for this is that it
requires more iterations for some reason.)

CMakeLists.txt

@@ -81,6 +81,7 @@ include (CMakeLists_files.cmake)
 macro (config_hook)
 	opm_need_version_of ("dune-common")
 	opm_need_version_of ("dune-istl")
+	opm_need_version_of ("ewoms")
 endmacro (config_hook)
 
 macro (prereqs_hook)