Use modular governance to manage the versioning system

[jstolarek]

This ticket is part of #48.

The versioning system is currently managed using the admin governance, i.e. requiring a signature from the master key. This needs to be changed - all the version management should rely solely on the updatable governance.

Note that updatable governance is now also stored in the versioning system. This brings up two important points:

1. Initialization, a.k.a. chicken and egg problem. It must be possible to insert the first version of the updatable governance into the versioning system without requiring approval from the updatable governance. This should be achievable using the Init Tokens.
2. Safety. It is now possible to update the governance to a new version, as well as invalidate existing governance. This opens possibilities of new fuckups that were not possible before such as invalidating all existing governance scripts, which would make a sidechain unmanageable. There's no really a way to prevent this, but we must make sure that the risks are clearly documented.

---

IOG Jira: https://input-output.atlassian.net/browse/ETCM-7871