Add object telemetry subscription to quad_control node

[pstrauch]

In order to track and pick up objects, we need access to the object's telemetry data in the quad control node.

Required steps:

• Create a suitable, thread-safe data structure which holds the object's telemetry data within the Quad class
• Create a subscription to the object's pose stream, where the callback populates the before implemented data structure

[pstrauch]

Addressed in #42.