statically allocate app container IPs

We removed httpPort with the assumption that docker allocated IPs
and kept them as long as the container is around. This turned out
to be not true because the IP changes on even container restart.

So we now allocate IPs statically. The iprange makes sure we don't
overlap with addons and other CI app or JupyterHub apps.

https://github.com/moby/moby/issues/6743
https://github.com/moby/moby/pull/19001

migrations/schema.sql

@@ -85,6 +85,7 @@ CREATE TABLE IF NOT EXISTS apps(
     taskId INTEGER, // current task
     errorJson TEXT,
     servicesConfigJson TEXT, // app services configuration
+    containerIp VARCHAR(16) UNIQUE, // this is not-null because of ip allocation fails, user can 'repair'
 
     FOREIGN KEY(mailboxDomain) REFERENCES domains(domain),
     FOREIGN KEY(taskId) REFERENCES tasks(id),