Refactor field writing

- Accumulate field data in a dictionary
- ASCII data
    - with keywords are stored in primitiveEntry objects
    - without keywords are stored in formattingEntry objects
- Binary data are stored in fieldDataEntry objects
- The IDs in the data.bp are names of the entries
- New feature: global uniform. Determine whether each field is uniform on all the ranks. Do it using a single reduce per GeometricField.
- For volFields the procPatch fields are removed from the IO
- For surfaceFields the procPatch fields are mapped into the global internal surfaceField and then removed