Port blocks need to be updated if a mechanism changes

[lizlooney]

If a component is added to a mechanism after that mechanism is added to the robot, the new port sockets on the mechanism block in the robot are not filled with port blocks.

Steps to reproduce:

1. Create a new project.
2. Create a new mechanism.
3. Add the mechanism to the robot.
4. Add a component to the mechanism.
5. In the robot, the mechanism block has the correct port socket, but there is no port block plugged into it.