When curtain user is spamming a lot of messages in a short amount
of time, mod need to scroll all the way up to the first spam message to
know who send those spam message, thus start banning them.
This patch add a context menu to open the sender detail dialog, it could
make banning the spam user and batch-deleting spam messages easier.
This is the first step in separation, so we can focus more on the
actions in this menu, and it's not tangled up in how the context menu is
shown and displayed.
For now everything should look identical. However this moves to using a model for the content of the message and is intended to lay the foundation for improved message content representation, e.g. splitting up a text message in multiple sections and using different delegates for things like code and quotes.
Move the functionality to cache the contents of a chat bar from the room directly and to a new ChatCache object. This works pretty much the same with a few extra check and balances, this also made it easy to put a test suite around the functionality so I did. The current functionality should be identical to what exists.
This is in prep for threads which will require managing even more caches if we create one per thread.
