Draft: Investigate support for many application shards

Story

This is:

• Based on !60088 (closed)
• Extends !61015 (closed)
• Resolves #329969 (closed)
• Partially addresses #328523 (closed)
• Partially addresses #329972 (closed)

This will:

• set-up 4 application shards
• use a single instance-wide database

To provision:

bin/rake db:prepare
bin/rails console

NamespaceShard.random_shard { User.create!(name: "ayufan", username: "ayufan", email: "ayufan@ayufan.eu", password: "aaaa1234", admin: true).update!(confirmed_at: Time.now) }

You can now create new top-level groups, and play with them.