implement multi-robot communication (swarm)

[previ]

implement a framework (api, server) to let bot communicate with each other when they are in the same group.
Ideally:

• robots can be configured to be part of a group (swarm)
• robots should be able to exchange messages (events) among the swarm population
• robots should be able to access a common data structure, with controlled read/write access

[previ]

after #77 this feature is on hold.