Improve line wrapping in messages

A user reported a bug I had in mind once but forgot about: messages consisting of one very large "word" don't get wrapped in the chat history. By sending a very large sequence of characters without spaces etc. you can essentially explode your window width.

Seems like this is really easy to fix: in briar-gtk/briar_gtk/widgets/private_message.py#L121 all we have to do is to add a new code line calling body_content.set_line_wrap_mode() with Pango.WrapMode.WORD_CHAR .