Add initialization of robot

[vetlek]

Describe the improvement you would like to see
Robots might need different types of preparations (localization etc) before they are ready to perform missions. These types of actions should be done before the robot starts a mission/is able to start a mission.

How will this change existing functionality?
A suggested solution is to add a def prepare(self, prepare_params) to the robot interface. A new state is created (either before entering idle or between idle and initiate_step) that make use of this function and depending on the result either aborts (notifies users that the robot is not ready) or continue to the next state.

How will this improvement affect the current Threat Model?
No changes