Display current theme in footer

I decided left justification looked best for footer and have set that in math3 theme.
Change VERSION to release/2.7
Change label -- assign new sets to current user

This doesn't change the behavior, which was already correct -- namely the new set was assigned to the current user.  This simply changes the label to read user    instead of 'none'.
Adjust appearance of homeworkset tables

Make text fit inside the text input boxes more neatly by using XXem as the unit of width -- set the width in math3.css
although it is also set inline for compatibility.  The font size is also reduced in math3.css for these tables.
Finally the labels for the checkboxes are removed and replaced by a link to the ProblemSetDetails page where the rest
of the data for the set can be edited.