fvOptions: Reorganized and updated to simplify use in sub-models and maintenance
fvOptions are transferred to the database on construction using fv::options::New which returns a reference. The same function can be use for construction and lookup so that fvOptions are now entirely demand-driven. The abstract base-classes for fvOptions now reside in the finiteVolume library simplifying compilation and linkage. The concrete implementations of fvOptions are still in the single monolithic fvOptions library but in the future this will be separated into smaller libraries based on application area which may be linked at run-time in the same manner as functionObjects.