Made title, cmsTitle and description properties translatable for widgets by using the _t() function
in the properties respective getters (using the static property as the default translation as not
to change the behaviour when no translations exist). Uppercase TITLE, CMSTITLE and DESCRIPTION
translation strings used...
Fixed by having Widget::CMSEditor return a FieldList (with fields from
getCMSFields) for showing DropdownFields and ListboxFields correctly,
and by using FormField::saveInto() for saving the data in
Widget::populateFromPostData().
