Added two alternative functions for chromatin movement,

they to the same job as their original version, but do
corrections differently -- no DT transform is used, but
just slow shift towards chromatin centre is used instead,
which is a lot faster (but seems to be a little error prone).

Added:
Cell::ChrMoveWithBrown() and Cell::ChrMoveByFlow() with no dmOfBackground parameter.

M    cell.h
M    cellChr.cpp