Add constants for RIF-CS v1.5 and fix naming

Add the ELEMENT_* constants required for
RIF-CS v1.4 and v1.5 and tidy up the ordering
of the constants. Make wording of comments
consistent. Remove the wrongly-added
constants ELEMENT_RIGHTS_INFO and
ELEMENTS_RIGHTS_TYPED_INFO.
Fix spelling of ELEMENT_EXISTENCE_DATES.