We have various "EntityId" formatters that conflate and combine functionality for formatting both EntityIdValues and EntityIds.

ValueFormatters for DataValues contain some specific behavior, like exception for DataValueMismatch which can take two arguments:

1. expected value type
2. actual value type that's attempted to be formatted

it would be odd for it to have multiple expected values, one of which is not actually a DataValue.

EntityIdValue formatters can reuse most/much of the EntityId formatter functionality but should behave more consistently as value formatters.

Version: master
Severity: normal
Whiteboard: u=dev c=backend p=5 s=2014-04-01