Fix DirectShowLib & nuget Package

Upgraded to .NET 9 (incl. .NET 8 compatibility), removed .NET Framewo…

…rk compatibility. If you are still using .NET Framework, please use Version 2.3.0 of WPF MediaKit!

- Fix wrong sound volume control

- Upgraded to .NET Framework 4.8
- Test Application with x64 support

Update README.md