The pre-job is meant to exit quietly if the prerequisite data is not
available yet. However, the epi pre-job check was raising an error
if AlternativeSuccessFileTemplate was missing from the config for
either Deposition or Environment. This is now handled quietly too.
CAUTION: This means the epi component will never raise an error
for missing input data, i.e., no email will ever say epi has failed to
run.

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.

reading NAME.nc files rather than NAME.txt files (#19)

A useful function in ProcessorUtils is subprocess_and_log, which builds a subprocess command and write its stdout and stderr to the log handler. Beforehand, failures only ever generated an error message, but there are some use cases where another log type is preferred. This adds a log type option to the function, and uses it in one case where a warning is more appropriate.

Initial commit. Currently only working for Nepal deposition and (partially for) Ethiopia environment v2.0