Create promisifed methods for methods with callbacks

[blimmer]

There are a few methods in the appboy library that take anonymous functions as callbacks:

• isPushGranted(yesCallback, noCallback, safariWebsitePushId)
• registerAppboyPushMessages(successCallback, deniedCallback, safariWebsitePushId)
• submitFeedback(replyToEmail, message, isReportingABug, successCallback, errorCallback)

To better integrate these with Ember, we should expose methods that bind to the Ember run loop and return an RSVP promise. For instance:

// addon/utils/promisified-methods.js

export function rsvpIsPushGranted(safariPushId) {
   ... logic ...
   ... returns a promise ...
}