Adding the ability to set the application display name in AppRatingFlow 

This is a new pull request from a different branch.  Same as #37 but moving the declaration outside of the #if so that OSX can use as well.

This would add the ability to set an application name other than the CFBundleDisplayName in the AppRatingFlow. This could close issue #36

The reason that I created this is because my display name for my application is shortened to 'wyc' but I would like the "Do you love %@" to say "Would you choose" rather than the display name.

This is just the way that I thought was the simplest solution to the problem.

I have not tested this in any mac applications only my iphone application and the ApptentiveDemo project.

Below is how I use it in my application.

ATAppRatingFlow *sharedFlow = [ATAppRatingFlow sharedRatingFlowWithAppID:@"x"];
[sharedFlow setAppName:@"Would You Choose"];
Let me know if this doesn't make sense or you think it should be done a different way.
Cheers!
-Kevin