Store "failed to send" messages

Whenever on 4g/mobile data and sending a text message where the connection drops, @Clyde pops in, removes the message and sais that "an unknown error has occurred" (this message could also be less generic, but that's not what this suggestion is about). Instead of removing the text that was sent, store it and let it be re-sent when connectivity is better. Typing out a response (especially on mobile) only to have @Clyde delete it is tiresome.