Introduced a 'TESTING MODE' in which user may override some internal

default settings of the simulator without having the need to adjust
the source code and to recompile it afterwards.

As a result: New section '[testing]' has been introduced into config files.
This section is mandatory but may be empty. Unlike the other sections, whose
content is fixed and must be strictly present, the content of this one is first
checked for presence and secondly, if found, certain action is taken (usually
overriding of default behaviour in the simulator).

Added sample full-featured configuration for the testing mode.
M    ISBI2015/config-smallVOI-lowSNR.ini

These files were modified to become sensitive to the testing mode configuration options.
M    src/main.cpp
M    src/cell.cpp
M    src/cell.h
M    src/cellScm.cpp
M    src/scheduler.cpp