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/apps_v1_get.go

@@ -0,0 +1,23 @@
+package server
+
+import (
+	"net/http"
+
+	"github.com/fnproject/fn/api"
+	"github.com/gin-gonic/gin"
+)
+
+// TODO: Deprecate with V1 API
+func (s *Server) handleV1AppGetByName(c *gin.Context) {
+	ctx := c.Request.Context()
+
+	param := c.MustGet(api.AppID).(string)
+
+	app, err := s.datastore.GetAppByID(ctx, param)
+
+	if err != nil {
+		handleV1ErrorResponse(c, err)
+		return
+	}
+	c.JSON(http.StatusOK, appResponse{"Successfully loaded app", app})
+}