Reduce the number of database queries in UserManager.
Thanks to Daniel Silverstone for the suggestion and patch.
This reduces the number of queries made for get_user and get_address methods and uses .one_or_none() instead of calling .count() and .one() separately which results in two database lookups.
The performance improvement of this change is small, but does reduce the code a bit too.
Closes #700 (closed)
Edited by Abhilash Raj