SpringLib - Provide event listeners

[mathze]

Is your feature request related to a problem? Please describe.
Currently we need to know that RF also supports certain events (e.g. testStarted).
It would be beneficial if the RobotLib would provide a simple way to register event listeners for the different events.

Requirements:

• (M): We can subscribe to all events RF provide, by calling "simple" functions
• (M): Support multiple listeners per event
• (S): Listener can be unsubscribe
• (M): Aligned with RF the execution of registered listeners is independent from each other
• (M): The data provided by RF should be mapped to appropriate structures
• (N): Listeners should not only run independent but also simultaneous to avoid one listener blocks execution of all others.

(M): Must
(S): Should
(N): Nice to have