Add getUser method to SecurityAwareTrait

## Add getUser method to SecurityAwareTrait, so that the user can be accessed with a method that is a verb, not a noun

### Acceptance Criteria
1. `user` method is renamed to `getUser`.
1. New `user` method is created as an alias to `getUser`. (To be deprecated in v2.0)

### Tasks
- Modify SecurityAwareTrait

### Additional Notes
- It is our convention that method names should always be verbs succinctly describing what the method does. Using a noun for the name describing what it returns violates this pattern.