Synnefo

Remove depricated settings and update migrations

Change and fix migration files

Change network migration, so that it does not allocate a new bridge to
existing network. Instead it keeps the bridges from the old NetworkLink
pool.

Remove network_mac_prefix migration because there are no networks with
mac prefixes....

Fix migration files

Fix south migration files. In data migrations, access the Models from
the orm, instead importing Models from synnefo.db. This is necessary as
the orm provides access to the version of the models that existed when
the migration file was created.

Print warning about subnet value during migration