Groupchat with coi user and non-coi user: differentiate between reply and reply all

[matthesatox]

Describe the bug
If a non-coi user takes part in a group chat, he is able to reply to all or to one group member via email. Reply to all means that the message is displayed in the chat for all, while just answering means that the message is only displayed for the individual recipient. However, in group chat context.

To Reproduce
Occurrence: always
Steps to reproduce the behavior:

1. Start a new group chat
2. Add coi user and non-coi user to group
3. Send a message in group chat
4. Non-COI user has to open his email client
5. Non-COI user replies to the message. As recipient is only one group member entered
   Actual result:
   The message appears in group chat context but only for one member
6. Non-COI user replies to all. As recipient are all group members entered
   Actual result:
   The message appears in group chat context for all members

Expected behavior
If a non-coi user replies to one member of the group, the message should appear in COI as single chat. Reply to all means that the message is displayed in the chat for all

Screenshots
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App information (please complete the following information):

• App version: 0.600.2 (515)
• Plugin version: [e.g. 0.4.0]
• Delta Chat Core version: [e.g. 0.40.0]
• Flutter version: [e.g. 1.0]

Smartphone (please complete the following information):

• Device: iPhone 11 Pro Max
• OS: iOS 13.4.1 final

Additional context
Add any other context about the problem here.

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