- avoid any operations for zero sources
- explicit sources are applied to the entire mesh can be added directly,
without an intermediate DimensionedField
- update some legacy faMatrix/fvMatrix methods that used Istream
instead of dictionary or dimensionSet for their parameters.
Simplify handling of tmps.
- align faMatrix methods with the updated their fvMatrix counterparts
(eg, DimensionedField instead of GeometricField for sources)