Create "Swarm-ful" collections like Set, List, and Map

[sanity]

Scala collections do not use Swarm references internally, which means that they cannot be split across multiple machines.

We need to create "Swarm-ful" versions of these collections that do use Swarm Refs internally.

[earldouglas]

For reference, see section 4.2.

[earldouglas]

I created the swarm.collection package to hold these.