Extend ObservableCollection with AddRange and RefreshItems methods

[hardcoder]

Is your feature request related to a problem? Please describe.

1. ObservableCollection does not contain AddRange method, but has Add method.
2. It also does not raise an event on item change, just only on item addition/removal.

Describe the solution you'd like

1. Add extension method AddRange
2. Add extension method RefreshItems

Describe alternatives you've considered

Additional context