Support extension of the Issue schema

[VJftw]

Feature

Current behaviour

The dracon issue schema support a generic set of fields related to an issue.

Disadvantages of current behaviour

• We cannot add additional metadata used in other systems. For example, there is no appropriate field a JIRA ticket ID.

New behaviour

Support extension of the Dracon issue schema to arbitrary namespaced fields.

New behaviour advantages

• Dracon issues can maintain state/data used by other systems in a namespaced manner. e.g. thoughtmachine.net/jira/ticket-id