Add a "No Messages" label to the TextSecureViewController

I've made a few changes to the Storyboard and the TextSecureViewController header and code files.  The app now has a functioning "No Messages" label to make the view a bit cleaner.  Design is definitely subject to change, but functionality is complete.
this isn't a bug currently as we only have one section, but you probably want a break; here (if your goal is to find the first section that hasRows), or to || your hasRows value with the boolean each time (if you goal is to find if any section has rows), or to && your hasRows values with the boolean each time (if your goal is to find if all sections have rows)