Feature surface field value operations

• add absolute weighting for surfaceFieldValue (issue #567 (closed)). Useful either for flow-rate weighting where backflow should be ignored or when surfaces have inconsistent orientation.

• support derived field pTotal for incompressible flow

changed the description

changed target branch from master to develop

assigned to @andy

added 25 commits

• 19f2e041...9b7110e7 - 22 commits from branch develop
• 31321271 - ENH: add absolute weighting for surfaceFieldValue (issue #567 (closed))
• 5c687ff9 - ENH: support pTotal as a derived field for surfMeshSamplers (issue #567 (closed))
• 42dff830 - ENH: a weighted operation without a weightField is an error (issue #583 (closed))

Compare with previous version

mentioned in commit 1fd2ba4c

merged