HWKALERTS-89 Normalize Incoming Data Format

- remove Availability, NumericData StringData and MixedData
- redefine Data to be used as the sole data format
  - let the ConditionEval impls deal with any conversion
  - provide convenience factory methods for when caller knows
    the data type he wants to provide.
  - Note, support for multi-value conditions (i.e. the 'values'
    field) is anticipated but not yet a reality.
- Make AvailabilityType a 1st class citizen
- Note: REST API CHANGE in sendData endpoint, but this is
  not [yet] used in Hawkular code outside of alerts.
- Update bus integration code (topic listeners) to use new
  mechanism

hawkular-alerts-api/src/main/java/org/hawkular/alerts/api/model/data/AvailabilityType.java

@@ -16,7 +16,6 @@
  */
 package org.hawkular.alerts.api.model.data;
 
-import org.hawkular.alerts.api.model.event.Alert;
 
 /**
  * Severity set for a {@link org.hawkular.alerts.api.model.trigger.Trigger} and assigned to an