Appcelerator, the company behind the popular Titanium app-building platform, is announcing its third acquisition today. The company is buying Cocoafish, a mobile app infrastructure provider that lets developers add various features to apps including messaging capabilities, push notifications, photo uploads, checkins and other social features, storage, discussion forums and more. Although the name implies an iOS affiliation, Cocoafish is actually a cross-platform backend service provider supporting iOS, Android, and even Flash and Ruby. Starting in Q2 2012, the features Cocoafish previously…