replaced NUnit with own test framework
improvements and cleanups

- CHG: code cleanups and improvements
- ADD: proetcted TimerInterval property for JobScheduler
compatibility, fixes and cleanups

- ADD: System.Collections.Generic.ISet<T> interface for compatibility
reasons
- CHG: code cleanups
- FIX: melder methods in ProxyBuilder class
minor changes
helper methods and cleanups

- ADD: FirstOrDefault() helper method with predicate
- CHG: code cleanups and improvements
- CHG: code cleanups
- FIX: minor fixes