As a developer, I want to create login/registration flow for users of my app.

[richk]

Use Parse to create login/registration flow for users of the app to sign in.

[richk]

The objective of this task is the following:

• Integrate with parse API.
  • Register app with Parse
  • Setup app to be able to post data to parse and view in parse data browser
• Create a login screen
  • Activity for logging in
  • User should be able to login if already signed up
  • If user does not exist, create flow to let the user sign up.
• Create a sign up screen
  • Activity for signing up
  • User should be able to sign up
  • TODO : email verification for users who wish to sign in using their emails.
  • TODO : handle error when username is already taken.

[richk]

Guys, please review this task with the code checked in and lice cap previews, so we can close it. \cc @madhurk @rcao137.