Fronetend simulation status indecator

Add an indicator on the frontend page to show
1. how many tasks are queued? 
2. status of the backend {idle, running, error happened}

Enhance the existing API Get /currentRunning in [server.py](https://github.com/UAVLab-SLU/DRV_public/blob/main/backend/PythonClient/server/simulation_server.py) to return the necessary information.