Generify user manager, remove unnecessary exceptions
Remove unnecessary exceptions, unnecessary fields
Add CAPA command for Pop3 (empty capabilities), load all commands in static initializer
Change JUnit dependency to compile scope, add GreenMailRule, use GreenMailRule in various test cases, separate GreenMailOperations from GreenMail implementation to allow creation of GreenMailProxy and GreenMailRule
Refactor GreenMailUtil, remove old stuff from Retriever
Remove dependency on testng
New constructor for rule with single server setup
Add getManagers to operations
Convert all unti tests to JUnit 4