Add flask-Migrate + alembic for automated database migrations.

Update some dependencies to their latest version.
Make executable scripts executable (chmod +x).

db_migrate.py

@@ -0,0 +1,13 @@
+#!/usr/bin/python3
+# -*- coding: utf-8 -*-
+from nyaa import app, db
+from flask_script import Manager
+from flask_migrate import Migrate, MigrateCommand
+
+migrate = Migrate(app, db)
+
+manager = Manager(app)
+manager.add_command("db", MigrateCommand)
+
+if __name__ == "__main__":
+	manager.run()