* added method mmv

* added default constructor and made necessary changes for is to work, i.e.
    * made members pointers instead of references
    * allocate memory internally for lowRankFactor_ if default constructed
    * add destructor and delete lowRankFactor_in destructor if internally allocated
    * adapt uses of member
* added non const getter method for lowRankFactor_

[[Imported from SVN: r5477]]