Implement step_status using currentMissionExecution(robotID)

[andchiind]

Describe the new feature you would like to see
The step_status ISAR function should be implemented. This is not a big priority since we do not run missions task-wise, but it might become useful in the future.

Describe the solution you'd like
We can use the currentMissionExecution(robotID) to get the current task status. Otherwise we will need to subscribe to the mission status.

How will this feature affect the current Threat Model?
N/A

[andchiind]

Implemented in #137