Add a workaround to get back to the home view

We've identified an issue while developing the tablet interface whereby in some occasions in the UI the two PageStacks don't work well together.

To reproduce:

- Tap on the Notebooks tab
- Tap on a notebook
- Tap on a note within the notebook

Result:

- The title of the note replaces the Tabs in the Header title, making it impossible to further navigate the app

Expected:

- The Tabs in the Header remain unmodified

We've discussed a workaround whereby we will show a button on all Toolbars to return home. This is to be used only during MWC as a fallback and will disappear once the SDK issue has been fixed. The Home button will only be shown in the tablet view, not on the phone one.