Fix user-facing helping term 'insecure' to 'unsecured' 

'Insecure' implies an uncertainty of intention or confidence. Unsecured is more specifically addressing the protocol which wraps the message delivered. This struck me immediately while feeling particularly vulnerable and texting someone with whom I experienced real-life drama, and I'm guessing this applies to many 'personal' text messages. Related to #1337 but the term 'unsecured' was never brought up.