Adding Login flow screens

@nickai @ndun

Added the screens for the login flow with all the needed buttons and text fields.

The first screen where you select whether you are a mentor/mentee is just a placeholder for now, but the three other screens are there in basic form and all the data we need is getting passed with intents.

Happy to clean this up and work on the UI on Tuesday when I'm back from Coachella, but all the basic functionality should be there to sign up as a mentee.

Thanks!