Adding a marker invalidates state of spiderfied cluster

[sibbl]

When a cluster is spiderfied and a marker at this location is added afterwards, it should either unspiderfy the open cluster (like the original Leaflet.markercluster does) or update the spiderfied cluster so that the new marker is included.

[fungiboletus]

Yes, the spiderfied cluster are not dynamic yet.

[cordovapolymer]

@yellowiscool @simison @FalloutPL @mordka @vitalik74 @rwwagner90 @brunolellis @maxvonhippel @Cadrach @undr @uniphil @valerio-bozzolan @rolanddu @adimasci @maxhoffmann BUMP!