Activity Search Form: make the activity_role more obvious by placing next to the contact name field

Currently the "assigned to / target to / created by" widget in the Activity Search Form is located towards the bottom of the form, but the widget affects the contact field at the top completely.

Also, modify the activity role labels to match the listing column headers (With, Added by, Assigned to). See attached screenshot w/ revised layout.
Default activity role (radio button) should be 'With'.