INT: coherent: enable serial write of volFields

- Tested by writing volFields with the icoFoam's cavity test case
(boundary file is still needed in polyMesh)

- ASCII field files have some formatting issues (writing is done with
dictionary::write)

- OFCstream now inherits from OCharStream; rename foam-extend flavored
member functions to OF equivalents

- New regIOobject virtual member function "writeToStream" allows to
construct OFCstream within GeometricField

- The heavy data is now given to an OFCstream in the Field class, not UList.
Doing this makes it simple to ensure that every rank will call
OFCstream::write for every field.