Add Parse SDK

- Add RibbitApplication class as entry point for the app and for basic configuration
- Follow these steps to import the Parse jar file *as a module*: https://www.parse.com/questions/importing-library-in-android-studio
- It is save to put the application keys under version cotrol: http://blog.parse.com/2014/06/30/parse-security-i-are-you-the-key-master/
Remove Parse test code
Show AlertDialog when sign up info is missing
Fix inputType for passwordField in SignUpActivity
Merge branch 'develop' into feature/backend-user-accounts
Add sign up against parse.com backend
Put emailField below PasswordField in SignUpActivity
Merge branch 'develop' into feature/backend-user-accounts
Fix indentation
Add login against parse.com backend
Add logout menuItem
Refactor duplicate code into navigateToLoginActivity()
Organize imports
Add progress indicator for background tasks
Merge branch 'feature/backend-user-accounts' into develop