Per page

Added an option, when user can choose a number of objects per page. Developer can add this option like inclusion tags {% perpageselect 10 20 30 %} and {% perpageanchors 10 20 30 %} where "10 20 30" are numbers of objects perpage (it can be absolutely divert numbers). I also use a django session for it
Should be:

    if paginate_by is None: