Delete app's local storage on uninstall

[mattyg]

It looks like local storage is persisted after an app is uninstalled, keyed by app name. This can cause unexpected behavior if an instance of the app is then installed later with the same name.

To reproduce:

• Install app with network seed "" and name "myapp"
• Open app and have it write data to local storage
• Uninstall app
• Install same app with network seed "1" and name "myapp"
• Open app
  (check local storage data and see it has been written to)