Added rigid movement of cells with SOFA.

Since routines from Cell::SOFA_MoveImportedToReferencePosition() and
Cell::SOFA_MoveInitialToReferencePosition() could have been reused for
the rigid movements, their become wrappers to some new helper BPs
moving functions.

M    src/cell_08_G2Phase.cpp		- added support for cell movement with SOFA
M    src/cell.h						- added docs to the new functions
M    src/cellSOFA.cpp				- guess what :-)
M    ISBI2015/config-smallVOI-lowSNR.ini		- introduced new testing parameter: "disable rigid movement"