Initial attempt to track oriented surface fields
These changes are an attempt to cleanly identify oriented surface fields, i.e. those where the value is signed according to the owner->neighbour direction e.g. the face flux.
Still to do:
- propagate through field mapping - ready to test
- simplify surfaceFieldValue function object - passed tests
- check other uses, .e.g. AMI?
- clean-up of dev statements
- rhoCentral[DyM]Foam solvers