DragNBatch, application, debugging, ForEach, collections, fixes, cleanups and improvements

- ADD: synchronized lists and dictionaries are serializable now
- ADD: started to make use of DebuggerDisplayAttribute
- ADD: ForEach() helper and extension methods
- CHG: action parameter of IGeneralList.ForEach()
- CHG: actionStateFactories structure for ForAll()/ForAllAsync() methods
- CHG: code cleanups and improvements
- ADD: Index property for IForAllItemExecutionContext<T> interface
- FIX: minor fixes
- ADD: SynchronizedDictionary can handle custom key comparer now
- ADD: Vars property to TMApplication class
- ADD: can select DragNBatch plugin now