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_delete.go

@@ -0,0 +1,21 @@
+package server
+
+import (
+	"net/http"
+
+	"github.com/fnproject/fn/api"
+	"github.com/gin-gonic/gin"
+)
+
+// TODO: Deprecate with v1
+func (s *Server) handleV1AppDelete(c *gin.Context) {
+	ctx := c.Request.Context()
+
+	err := s.datastore.RemoveApp(ctx, c.MustGet(api.AppID).(string))
+	if err != nil {
+		handleV1ErrorResponse(c, err)
+		return
+	}
+
+	c.JSON(http.StatusOK, gin.H{"message": "App deleted"})
+}