Support code for Manager authorization of refunds

UserEntity.java: added JPA named query for manager-or-higher lookups

Hasher.java: Moved password-hashing function to a separate, single-responsibility utility class.

HasherTest.java: Added a unit test for Hasher#hashPassword

LoginBean.java: Updated to use Hasher.java

MainMenuBean.java: filled out stub "createRefund()" method; the Main Menu view now needs a form to fill in the "authorizingManagerUsername" and "authorizingManagerPassword" properties of mainMenuBean.