Developing the Serverguide using the rolling release model and rethinking String Freeze

We are proposing the following:

Developing and publishing the Guide based on the rolling release model. This implies:
- Official releases of the Guide will be LTS-only
- Unofficial publications based on snapshots of the interim development branch (available online)

Removing String Freeze and publishing links to some languages on help.ubuntu.com. This implies:
- A more flexible and realistic cooperation between contributors, committers, and translators
- All translations may not be published in the snapshots

Rationale:

- The development work being done every 6 months is not worth the administrative overhead required. Community involvement is simply not enough to warrant a publication every 6 months.
- Ubuntu Server installations tend to be LTS anyway.
- Based on observation, translators find the current string freeze schedule too aggressive.