Fixes to Streams row_m

Includes:

- Aliasing of created_by so we can have other joins with the users table in there.
- Field type hooks that allow field types to hook into the $sql.
- Fix so $stream_fields is only asked for once. It is still cached, but this just makes it easier.
Updating user field to use joins.
Simplifying the created_by join call in the get basic streams call.

This model call is used when we need basic data for the back end, so we are now just adding a join and using the user id and the username for displaying created_by.
Updating relationship field for new join syntax.

Now the relationship field adds to the join and grabs the join array and formats it for the plugin. Remains the same on the back end.
Minor code formmating