Finalize all existing features and pages

[endernoke]

Auth

• Welcome screen
• User authentication (signup, login, logout)
  • Basic functionality
  • Handle auth-related errors in UI properly (invalid credentials, email already in use etc.)

Home

• Add Soular stories (optional)
• Add profile button

Events page

• Show list of organizers/participants (like followers list in Instagram)

Profile page

• Ability to change profile picture
• List of post and event history, like the one in App Inventor
• Bio/self-introduction (optional)