Merge ofxiOS and ofxAndroid where possible

Some thoughts, i'm thinking it would be great to merge parts of ofxiOS and ofxAndroid together. They have a lot in common, and it would be great if creating an app for iOS would be rather easy to port to android, and vice versa.
A goal would be that most of the examples in iOS examples folder should also be able to run on Android.

Currently they both have each their own addon-ish baseapp sub-class, could we merge their commons into a ofBaseMobileApp class in the core instead? The naming in the two classes are not the same, so it requires some renaming, but i think for the better.

By doing this it might also help with better differentiation between core code for non mobile and mobile devices, using the namespace ofBaseMobil.

In my opinion now would be a good time to do it. ofxAndroid is going through a larger refactor with #4260, and it would be great with more examples for it.

Compare the ofxiOS and ofxAndroid addon-ish baseapp subclasses, their naming, and the core area where a shared ofBaseMobileApp could live. Review the mobile examples, especially the iOS examples targeted for Android compatibility, alongside the ofxAndroid refactor in #4260. Done would mean a coherent shared mobile base and examples that can run on both platforms.