Package restructure

[mmihic]

Pulls each subsystem (cluster, mapping, conn) into its own package and provides better decoupling between them.

R: @robskillington @xichen2020

[coveralls]

Coverage decreased (-1.2%) to 91.283% when pulling 12e8d6c on mmihic-package-restructure into dff8d0d on master.

[robskillington]

Do we need a test to cover this case?

[robskillington]

LGTM other than minor comment.

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