User-based group chats [15d]

[bart-at-mobicage]

• Change the plus icon to a pen (like telegram/whatsapp/messenger/...) (iOS only)
• Make it possible to
  • start a group chat
  • set/change an avatar and topic (admin)
  • add/invite friends to this group chat after it's created (admin)
  • change admins (admin)
  • remove members (admin)

[RubenMattan]

backend / android are ready to be validated iOS should better be done by another person the validate all the code etc..