This prevents trying to access the same group metadata in different groups.
Also, the conversation does not need to be reloaded once introduction messages arrive.
Closes#535
When a contact is added, her personal blog will also be added automatically.
Also, when a new identity is added, a personal blog for that identity is created.
Part of #436
Removes teaser and makes body mandatory.
It also adds support for deleting blogs and
introduces a getAuthorStatus() method to the IdentityManager
that takes a running transaction.
