Sign out user patch

[LucientZ]

Simple patch to handling AsyncStorage when values come back as falsy from either Firestore or AsyncStorage. Also added more succinct messages to inform a developer what is happening.

Changes

• For signOutUser(), the argument hasExpoPushToken has been renamed to deleteExpoPushToken to more closely reflect what the argument actually does
• Anytime a user is fetched, the user data is checked whether it is undefined. If it is, log a warning and set info as undefined
  • This also means the user will return to the login screen now when their data does not exist in Firestore.
• Error handling for removing an expo push token that doesn't exist (Though, I don't believe this was actually an issue. The app works as intended when I added it though, so it stays :P)
• Added icon to logout button in settings

[JasonIsAzn]

looks good! feel free to merge.