Basic auth form with Google OAuth implementation

[mjurkus]

Added screen where all authentication forms will be accessible.

• when skipping auth user will be authenticated as guest
• not sure about email prefilling from user's contacts? Do we need it at all?

Design is something to be desired, but polishing could be done later. Screen 1 Screen 2

[mjurkus]

Removed email lookup functionality. From API 26 Android suggests autofill based on autofillHints either way.