Merge Island Manager into Island (Composition is fine)

[drassaby]

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Previously, IslandManager was a single point of failure for our program and increased complexity. We should be able to merge the necessary logic into the Islands and communicate over some form of gossip protocol. This will ease our shift into K8s and help us start moving away from Akka. The other goal here is also to ease deployment in general, as now every separate running JVM is identical (except in solution space)