ENH: Enable coherent XiFoam/icoFoam parallel run

- Enable parallel runs with XiFoam and icoFoam in coherent format.
  Reading and, thus, startup is supported only from uniform fields.

- Refactor IOobject. Trait is_coherentIOobject is now used directly in
  typeHeaderOk() with SFINAE. Often the header and object type is
  checked via a base IOobject and the type is provided via the function
  template parameter:

    IOobject header
        (
        ...
        );
    header.typeHeaderOk<volScalarField>(true);

  The change allows to move the corresponding logic from GeometricField
  back to IOobject.

- In the two solvers, disable processor directories check by argList
  that otherwise leads to a fatal error.