[AC-3025] Android: UI - density-based images don't work on buttons & annotations

Problem

Using the instructions in the wiki guide at [Using density-specific resources on Android](https://wiki.appcelerator.org/display/guides/Using+density-specific+resources+on+Android), I added my icons in Resources/android/images/res-mdpi/media/icons/. I see that all the icons are getting copied to the build/android/res/drawable-mdpi directory correctly but when I run the app the icons which were used on buttons & as annotation markers don't show up. The following results in a transparent button:

Ti.UI.createButton({image: '/images/media/icons/buttonicon.png'})

Similarly, the following results in a transparent annotation which is clickable, but not visible:

Ti.Map.createAnnotation({image: '/images/media/icons/marker_pin.png'})

All other density-specific icons used in the app work correctly.

Discussions

* my question in the Q&A: [Density-based images don't work on buttons & annotations](http://developer.appcelerator.com/question/129524/density-based-images-dont-work-on-buttons--annotations) * somebody else seems to have faced a similar issue with annotations: [Density specific graphics for Android Map Annotations](http://developer.appcelerator.com/question/123062/density-specific-graphics-for-android-map-annotations)