Added a few importing and exporting functions in the importexport.*

files. Basically, they only import/export point coordinates to/from
given text files now.

M    CMakeLists.txt
A    src/toolbox/importexport.cpp
A    src/toolbox/importexport.h

M    src/cell.h         - some typos in the docs corrected
                        - added declaration of ScmXYTranslationalMovement()
M    src/cellScm.cpp    - added implementation of ScmXYTranslationalMovement()
M    src/cellChr.cpp    - removed debug report related to the RandomWalk initialization of chromatin