Cleanup: Replace dicts with models, strings with enums

Fix: Explitely only support Python 3

Change: Hide CLI subscriptions behind `--beta` argument

Fix: Setup requires underscores in names

Chore: Update aleph-message version requirement

Chore: Require newer aleph-message

Chore: Switch default API to api2.aleph.im

Chore: New aleph-message supports mounts

Feature: Add API to VM cache on host

Fix: Always ignore device.key files