Extend e2e tests

[nicodh]

This list should NOT show everything that could be tested, but focus on important use cases. Order should reflect priority.

• deleting a message should remove it
• create a group with 2 people
• remove someone from a group
• add contact by mail
  • confirm request
  • reject request
• use cases for a non chatmail address (warnings etc.)
  • test for auto encrypt
• what else...?

[WofWca]

• MessageList scrolling-related stuff, namely:
  • Typing a multi-line message makes chat scroll up (then you have to scroll to see new messages) #3763
  • Adding a reaction makes the chat "scroll up" (then you have to scroll to see new messages) #3753
  • Scrolling down on each new message in general (related: We don't scroll to some newly arrived messages #4329)