Restrict Unsent SMS Text to its Message Thread

Currently entered text (an unsent SMS message) persists when navigating between different contact threads on the web portal. This causes a high risk of accidentally sending sms text to the wrong person--just did this!

- If SMS text is entered but not sent have it only appear for that contact as a sort of 'draft'. Even just clearing the text when navigating between threads would also be preferable to current implementation