Added a UI element to indicate extension support of the chatroom. For
all groups it will always be red since we do not support extensions in
groups. In a 1-1 chat the indicator will either be green/yellow/red
depending on if the friend has support for all/some/none of qTox's
desired extension set.
* Added new negotiating friend state to allow delayed sending of offline
messages
* Added ability to flag currently outgoing message as broken in UI
* Reworked OfflineMsgEngine to support multiple receipt types
* Moved resending logic out of the OfflineMsgEngine
* Moved coordination of receipt and DispatchedMessageId into helper
class usable for both ExtensionReceiptNum and ReceiptNum
* Resending logic now has a failure case when the friend's extension
set is lower than the required extensions needed for the message
* When a user is known to be offline we do not allow use of any
extensions
* Added DB support for broken message reasons
* Added DB support to tie an faux_offline_pending message to a required
extension set
Blocked status will represent friends who are removed from Toxcore, but who still exist in UI and can be readded to Toxcore at a future time using their public key. Blocked friends are similar to offline friends, but have a different status icon and will be seperated in the friends list.
