(cherry picked from commit 0f5e125a)

wiring in the newly separated post_processing module into coordinator, rather than the plotting module

1) There is now a python alternative to the R-based wheat-source-
generation, called source_gen. The functionality to call source_gen
has been added (see ProcessorSurveys.pyL939 and L1032-1040), but not
yet switched on while we await testing of
output at the Met Office.

2) ProcessorComponents was huge (2100 lines!) and the structure was
not apparent. Each component's supporting functions are now in a
separate directory. There is also a ProcessorServer.py relating to
file down/up-loads. ProcessorComponents is now essentially a directory
 to import all the functions. This might inspire a more systematic
 (object-oriented?) structure for each component within coordinator
 in the future.