Convert chart legend dialog to widget UI

Conflicts:
	chart2/AllLangResTarget_chartcontroller.mk

Change-Id: Ibc265efe5a8bdf3e0e5fb8135fb0487de7e96764
Reviewed-on: https://gerrit.libreoffice.org/7199
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>