Warn user that they won't be able to sign back in if they sign out while offline

[gino-m]

Currently we only warn that unsynced data will be lost. We should also inform the user that:

• Offline surveys will no longer be available until their sign back in
• They won't be able to sign in until they're back online

@amegantz Suggestions here?

[amegantz]

If you sign out:

• Any unsynced data will be discarded
• You won't be able to sign in if you’re offline
• Offline surveys won’t be available until you sign in again

Are you sure you want to sign out?

[jcqli]

Need to add that you can't log back in if offline