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/datastore/sql/migrations/16_add_fns.go

@@ -0,0 +1,41 @@
+package migrations
+
+import (
+	"context"
+
+	"github.com/fnproject/fn/api/datastore/sql/migratex"
+	"github.com/jmoiron/sqlx"
+)
+
+func up16(ctx context.Context, tx *sqlx.Tx) error {
+	createQuery := `CREATE TABLE IF NOT EXISTS fns (
+	id varchar(256) NOT NULL PRIMARY KEY,
+	name varchar(256) NOT NULL,
+	app_id varchar(256) NOT NULL,
+	image varchar(256) NOT NULL,
+	format varchar(16) NOT NULL,
+	memory int NOT NULL,
+	timeout int NOT NULL,
+	idle_timeout int NOT NULL,
+	config text NOT NULL,
+	annotations text NOT NULL,
+	created_at varchar(256) NOT NULL,
+	updated_at varchar(256) NOT NULL,
+    CONSTRAINT name_app_id_unique UNIQUE (app_id, name)
+);`
+	_, err := tx.ExecContext(ctx, createQuery)
+	return err
+}
+
+func down16(ctx context.Context, tx *sqlx.Tx) error {
+	_, err := tx.ExecContext(ctx, "DROP TABLE fns;")
+	return err
+}
+
+func init() {
+	Migrations = append(Migrations, &migratex.MigFields{
+		VersionFunc: vfunc(16),
+		UpFunc:      up16,
+		DownFunc:    down16,
+	})
+}