Swarm conversations: make "Contact left" conversations read-only

Conversations in which all the participants have left can no longer be used and we should reflect this status. For now, for dialogs, we SHOULD strive to have only one conversation present at any given time. This may not always be the case, for instance, if:

• multiple devices add conversations with the same contact prior to syncing with each other
• if A has a dialog with B in which B leaves, A's conversation with B becomes read-only, but then if B then re-adds A , A will have a second non-read-only conversation

A read-only conversation is represented by:

• not making outgoing interactions(messaging and calls) possible
• provide a description for why the conversation is in the read-only state
• provide buttons allowing to
• a) remove the contact
• b) restart a new conversation with the contact

added SprintIn progress label

mentioned in commit f05ffbce

changed the description

marked the checklist item not making outgoing interactions(messaging and calls) possible as completed

changed the description

marked the checklist item provide a description for why the conversation is in the read-only state as completed

marked the checklist item provide buttons allowing to as completed

mentioned in commit a45754ed

removed SprintIn progress label

closed