Fix ViewModel key generation + Fix ViewModel scope handling

[arnaudgiuliani]

• ViewModel key is calculated against Key and/or Qualifier
• ViewModel is only created against root Scope to avoid any leaking (leaking Activity or Fragment ...). This fix the visibility problem, where ViewModel could have access to incompatible scopes.
• ScopeViewModel to help work on ViewModel scope like follow:

module {
    viewModelOf(::MyScopeViewModel)
    scope<MyScopeViewModel> {
        scopedOf(::Session)
    }    
}

class MyScopeViewModel : ScopeViewModel() {

    // on onCleared, scope is closed

    // injected from current MyScopeViewModel's scope
    val session by scope.inject<Session>()

}

Fix #1750