swarm: link trust requests and conversation's requests

This is only to avoid to return weird states from the daemon to the
client. But if a conversation is added through addContact,
removeContact should be called to removes it. However, if
removeConversation() is called, the conversationId in contact's
details MUST be updated.
Same for acceptConversationRequest, this should removes related
trust requests

Change-Id: I4b273075862cdcdffc7f13c1b5e581a2eebc411d