Update changelog with current patches

[nickvergessen]

Added

• Shortcuts have been added when a call is active: (m)ute, (v)ideo, (f)ullscreen, (c)hat and (p)articipant list
  #730
  #750
• Allow users to chat in multiple tabs in multiple chats at the same time
  #748
• Guest names are now handled better in chat and the participant list
  #733
• Users which are participanting in a call now have a video icon in the participant list
  #777
• Unread chat message count is now displayed in the room list
  #806
  #824

Changed

• It is now possible to join a call without camera and/or microphone
  #758
• Chat does now not require Media permissions anymore
  #711
• Leaving a call will free up the Media permissions
  #735
• Participants can now be @mentioned in the chat by starting to type @ followed by the name of the user
  #805
  #812
  #813

Fixed

• Correctly catch the input on the chat in firefox (instead of writing to the placeholder)
  #737
• Keep scrolling position when switching from chat to call or back
  #838
• Delete rooms when the last logged in user leaves
  #727
• Correctly update chat UI when leaving current room
  #743
• Various layout fixes with videos and screensharing
  #702
  #712
  #713
• Fix issues with users that have a numerical name or id
  #694
• Fix contacts menu entry when no user was found
  #686