Add support for Function and Trigger domain objects (#1060)

Vast commit, includes:

 * Introduces the Trigger domain entity.
 * Introduces the Fns domain entity.
 * V2 of the API for interacting with the new entities in swaggerv2.yml
 * Adds v2 end points for Apps to support PUT updates.
 * Rewrites the datastore level tests into a new pattern.
 * V2 routes use entity ID over name as the path parameter.

api/models/error_body.go

@@ -1,11 +1,11 @@
 package models
 
-type ErrorBody struct {
+type Error struct {
 	Message string `json:"message,omitempty"`
 	Fields  string `json:"fields,omitempty"`
 }
 
 // Validate validates this error body
-func (m *ErrorBody) Validate() error {
+func (m *Error) Validate() error {
 	return nil
 }