Close Conversations from Contact view

Add the option to close a Conversaion from the Contact view. So, after replying to an email in the Actitiy tab, for example, we can then mark the Conversation as closed, if required.

This is similar but not the same as the idea here: https://community.hubspot.com/t5/HubSpot-Ideas/Editable-conversation-status-through-workflows/idi-p/760625