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/server/trigger_update.go

@@ -0,0 +1,41 @@
+package server
+
+import (
+	"net/http"
+
+	"github.com/fnproject/fn/api"
+	"github.com/fnproject/fn/api/models"
+	"github.com/gin-gonic/gin"
+)
+
+func (s *Server) handleTriggerUpdate(c *gin.Context) {
+	trigger := &models.Trigger{}
+
+	err := c.BindJSON(trigger)
+	if err != nil {
+		if models.IsAPIError(err) {
+			handleErrorResponse(c, err)
+		} else {
+			handleErrorResponse(c, models.ErrInvalidJSON)
+		}
+		return
+	}
+
+	pathTriggerID := c.Param(api.ParamTriggerID)
+
+	if trigger.ID == "" {
+		trigger.ID = pathTriggerID
+	} else {
+		if pathTriggerID != trigger.ID {
+			handleErrorResponse(c, models.ErrTriggerIDMismatch)
+		}
+	}
+
+	triggerUpdated, err := s.datastore.UpdateTrigger(c, trigger)
+	if err != nil {
+		handleErrorResponse(c, err)
+		return
+	}
+
+	c.JSON(http.StatusOK, triggerUpdated)
+}