Byron/security key

Add Alert Dialog prompting user for a security key to access the rest of the app (as an added security feature).
- Alert Dialog appears after salesforce login and before the main activity view is launched. 
- Alert Dialog only appears when the security key that is stored in SharedPreferences is either null or no longer correct.
- If the user enters the incorrect key, the dialog will trigger a cycle of "error" and "retry" dialogs until the right key is entered.
- When the correct security key is entered, it is written to SharedPreferences so that the user will not have to reenter the key again (unless the key is changed.)

Maybe add a short description on what utils is