[feature] Implement clustering feature #114

[totallynotvaishnav]

To do

• Update docs
• Add tests

closes #114

[nemesifier]

Looks good, I will have a closer look tomorrow, in the meanwhile I can notice there's no mention of this feature in the README section in which the demos are listed (Different demos).

[nemesifier]

So, in the context of the map for OpenWISP, how can we cluster nodes which have different status (online, problem, offline, unknown) without losing the power of the overview of the map?

The map is useful to visualize the network on the map and know at glance if there's any area which is not working.

If we cluster all the nodes only in 1 cluster, without differentiating anything, we lose this powerful feature.

How can we cluster only nodes of the same type? That is, cluster the active node together, then the problem nodes, the offline nodes, the unknown nodes. So that when the map is viewed, the user knows how many nodes are experiencing problems.

With the current clustering I see on openwisp/openwisp-monitoring#433, this information is lost.