add only "modtype_X", not "X" class to activity li

Currently the name of the module gets added as a class to the li in the
courses list of activites/resourses e.g. li.activity.label.modtype_label
or li.activity.scorm.modtype_scorm

This change only outputs the modtype_X not the bare mod name.

It also changes a couple of bits of CSS and JS that were looking for the
old version.