BC break: default session builder should be the model manager

[sanpii]

https://github.com/pomm-project/pomm-bundle/pull/55/files#diff-fa25a4dfbe23ca7ad37b0906a8feba42L45

[mvrhov]

This was done on purpose:

• so there is no deprecation notice
• so the service is used instead

So this should be fixed differently IMO, the service should be used by default!