Ert 437 unify rml implementations

Content of this PR:

1. The old rml_enkf module is moved to a deprecated/ subdirectory. The rml_enkf_imodel module is renamed rml_enkf - this is now the only module performing rml.
2. The rml_enkf module has aquired some new options; including a use_prior setting which when set to false can be used to recover the behaviour of the old rml_enkf module.
3. The rml_enkf module has been tigthtened up with respect to missing realisastions; the dreaded "size mismatch" should now be history.
4. Many code formatting changes througout.