XTCE13 — Re-architect XTCE alarm model

XTCE alarms are associated with data types and come in a default and context set form. A variety of alarm types are associated with each data type, some specific to it (such enum alarms). However this is too restrictive to meet the needs of many of organizations. Specifically the following is requested: allow set of alarms without a required context by data type. Original reporter is JPL.