Operator ergonomics

[angrynode]

This PR makes table operators more ergonomic so:

• you can switch table directly from an operator, eg content_folder_operator.torrent()
• you can log directly from the table operator with log_create, log_update and log_delete methods

This requires the table operator to implement Deref<Target = DatabaseOperator> and TableOperator which has a single method fn table(&self) -> Table to save the table information in the logs.

This PR also reduces allocations when switching tables because we don't have to clone the state/user every time, by introducing a lifetime for table operators. That means a table operator can only live as long as the inner DatabaseOperator, which is perfectly fine.