Display wallet version and update status information

[pablen]

Besides triggering a notification once an update was downloaded it would be nice to display more detailed information about the wallet version and update status as many apps do. E.g. Google Chrome:

Some ideas:

• Display if user has latest version installed
• Display if an update is available and its download progress
• Display if an update was downloaded and is waiting for a wallet restart to be applied. Also provide a button to trigger a restart.
• Provide a button to manually check for updates