Renamed CanReload param on SetNavState to isLoading as that's the value passed through from `Cef`
Add IsLoading property to NavStateChangedEventArgs (inverse of CanReload)
Whilst `CanReload` is the inverse of `IsLoading` I think from a support point of view it's easier to have both as users are looking for some sort of loading flag
Reanme SetNavState to SetLoadingStateChange (Internal method rename, to keep inline with `Cef` API, no external naming changes so shouldn't affect user, just makes it a little easier when looking at the Cef documentation)