Model for thermal dispersion.
- input fields for longitudal and transversal dispersivity
Fix wrong calculation of dispersive tensors (heat, concentration transport).
- difference from reference manual caused by misplacing microscopic velocity by flux
Implemented thermal sources in heat transfer.
Modified meaning of concentration sources.
 - now they are multiplied by cross section, so that input fields are in natural units independent of computational domain's dimension
Documentation of heat transfer + corrections in doc of transport.
- updated according to some recent model changes in source code
Merge branch 'master' into DF_bih_tree