Added field for date shifting
Merge branch 'newbutton2' into dateshift

Conflicts:
	htdocs/themes/math4/math4.css
Added date shift field.  When its nonzero the dates of all imported homework sets are shifted so that the earliest due date is set to the shift field.
fixed unintended change
another unitnended change
Merge pull request #219 from goehle/dateshift

Shift Import Dates