Bug 918970 - display existing thread when sending a sms from contact app

please move this in a separate function, for example `findThreadForNumber`

This function would return a promise, resolved with `viewInfo` once it's ready. This way you'll be able to do something like: `this.findThreadForNumber.then(this.toView.bind(this))`.

Please put all anonymous functions in a separate named functions (they can be defined inside the new function `findThreadForNumber`).