Improved automatic validation updating with ValidatingObservableColle…

…ction

Added validation features; bugfixes

* Increased .NET Framework requirement from 4.0 to 4.5 for INotifyDataErrorInfo
* Property cleanup support is experimental and may be changed later!

Support for transitively dependent get-only properties

Fixed: Auto-properties from VS2013 Debug build not recognised

Fixed DependsOn attribute processing (wrong type of constructor argum…

…ents)