Added two functions Cell::SOFA_InitialExport() and Cell::SOFA_NextImport(),

which are implemented in the new file src/cellSOFA.cpp. This is related to
the SOFA framework interconnection.

The functions provide easy way to export various data from the simulator
and to import subset of the data back to the simulator. Most of it is
controlled via the configuration file into which a new section "[sofa]"
has been introduced. This section is only mandatory iff SOFA feature is
turned on in the CMake.

M    CMakeLists.txt		- acknowledges the new cellSOFA.cpp file
A    src/cellSOFA.cpp	- SOFA export and import functions
M    src/cell.h			- added their declarations (with poor doc for now)
								- initialization of Cell::chrCentres is now in
								  the cell's constructor
M    src/cellChr.cpp		- the init of chrCentres has been removed from
								  the Cell::ChrInitialDistribution()

M    ISBI2015/config-smallVOI-lowSNR.ini	- a sample of the [sofa] section