Binding on dynamicRes are not updating

## localize is not working in our app

We use strings in dictionnary and all elements are refreshed into the new strings when we change the dictionnary but not the datagrid headers (not mahapps) and the hamburger menu... Tabs are working with some other controls

## Steps to reproduce
with the demo app, include the stringManager joined

and 2 dictionnaries in the folder \Resources\XAML\Languages
change as resource

include one of them by default in the app.xaml

``

bind a menuitem to a string in HamburgerMenuDefault.xaml
```

```

and bind also the tabs in HamburgerMenuSample.xaml
```

```
in the app start call to change the culture from FR to US

```
protected override void OnStartup(StartupEventArgs e)
{
base.OnStartup(e);
StringManager.Instance.SetCulture("en-US");
}
```

bind a command in the menu to change back

` this.ShowProgressDialogCommand = new SimpleCommand(o => true, x => StringManager.Instance.SetCulture("fr-FR") ); //this.RunProgressFromVm()`

work in the tabs but not in the hamburger

## Environment

```
MahApps.Metro version: all last RC
Target Core 8

Reproduce the issue in the demo app using HamburgerMenuDefault.xaml and HamburgerMenuSample.xaml, with the two language dictionaries and StringManager.SetCulture calls described. Compare the updating TabItem bindings with the non-updating HamburgerMenuGlyphItem and datagrid headers, then trace the relevant binding behavior. Done means the hamburger menu and datagrid headers refresh when the culture changes in both directions.

Written by the indexing model from the issue text.