Add passcode login screen

[jeff1evesque]

On a similar note as #205, this application should implement a passcode lock. If someone goes to another application on the iOS device, and returns, they should be prompted with a passcode, or maybe a thumb print scan. This should be similar to Dropbox's implementation:

[giraam]

+1

And not only for premium accounts, please! It's a matter of privacy and security.

[thedillonb]

I think this is a wonderful idea. And to @giraam's point, I'd make it available to everyone.

[MaXFalstein]

Can this include TouchID for the TouchID iPhones? Thank you!

[MaXFalstein]

@thedillonb - four and six digit passcode and custom length passphrase would be great.

An extension could be to add CodeHub specific Google Authenticator based two step authentication.