Progress spinner needed to indicate that a task is in progress e.g. changing the active wallet

[nickrod]

Android v1.1.0

Steps to reproduce:

1. Click the drop down to select a wallet.
2. Select a different wallet.
3. After authenticating it appears to hang and shows a blank screen with "Enter Password" on top.

I noticed on most of the screens when an action is taken it will just pause for a few moments as it processes, but there is no indication to the user that anything has happened. There should be an indication when something is happening in the background.