Option to hide codes (copy/paste only)

**Describe the feature you want:**
Option to visibly hide all OTP codes in popup, click-to-copy should still function as normal by clicking issuer/account name.

**Why do you want this feature in Authenticator?**
I frequently demo systems that require OTP input as only login method, however for larger crowds this dramatically increases the possibility of an opportunistic shoulder-surfing attack. Hiding the codes negates this issue.