Added a new cell descriptor: Cell::scmCellPolarityVector.

M    src/cell.cpp		- Both initial cell mask creating functions (called from
							  the Scheduler's constructors) now also init the polarity vector
							- added implementation of GetCellPolarityAndCentreVector(),
							  which is basically a SVD calculation over given mask image
							- GenerateCentrosomes() now makes use of the above function

M    src/cell.h		- add the Cell::scmCellPolarityVector and Cell::ScmResetCellPolarityVector()
							  that updates it
							- added declaration for the GetCellPolarityAndCentreVector()

M    src/cellScm.cpp	- implementation of Cell::ScmResetCellPolarityVector() that
							  also uses GetCellPolarityAndCentreVector()