Telegram strikethrough text

Consider that a Telegram user applies a "strikethrough" formatting to their text.

When this text gets transmitted over to XMPP, it doesn't gets formatted properly. We should fix it somehow.

One possible solution is to use the unicode strikethrough (which, honestly, looks like dick), and another one is to prepare properly formatted messages according to XEP-0393 (still experimental, so most likely will look like a dick in most of the XMPP clients, though).