Change interface export step 1

[mamueluth]

This showcases for example 1 how the changes proposed in this PR would affect the hardware. The adjusted example has been tested and works with the changes. If you want to test them, first checkout the branch from the before mentioned PR.

The changes are described in more detail in the PR:

• Storage for Command-/StateInterface is moved to the SystemInterface -> no local vectors of commads/states
• There is now a default implementation for exportation of the Command-/StateInterfaces -> removed export_state_interfaces() and export_command_interfaces()
• SystemInterface provides getter/setter methods to update states/read commands. Can either be used with the by passing the InterfaceDescription or state_interface-/command_interface-name