Get Packet path for simulation API

[PopBogdan97]

Here we have to discuss how to simulate the packet transmission. E.g.:

1. GUI -> Send "transmit the first packet"
2. Backend computes the behaviour
3. Backend returns the path of the first packet
4. GUI -> shows the behaviour

OR

1. Backend computes all the paths for the packets (including various events)
2. GUI -> Show all the packets' behaviour without interruptions

[zanna-37]

My idea is that:

• the GUI enqueues and Backend_event that states the intent of sending a packet.
• The backend will take care of doing it, including calculating the path, etc. (as a router/endpoint should do).
• When the packet has been sent, the backend will enqueue a UI_event that asks the GUI to animate the sending.