Decouple Shadow logic and replace Android default StateListAnimator

The original motivation for this release is to make room for a new plugin to apply shadows to non Angular projects.
Turns out the complete overhaul will belong to a next release.
This is also fixing #10 regarding StateListAnimator for Android buttons.

Density Independent Pixels / TranslationZ

1. BugFix: Integer directive not rendering on iOS.
2. Density independent pixels: Now you no longer have to worry about providing the correct values for pixel related attributes based on the device's screen density. Since iPhone 6S, each point correspond to 9 device pixels (3 horizontally x 3 vertically - that's the reason behind the @3x images - view more here). The same happens to Android where the benchmark (mdpi) is considered ~160 pixels (or dots) per inch (dpi) and the majority of the modern devices having way denser screens, reaching ~640dpi or more. Find out more here.
3. New Android specific attribute called translationZ. The elevation attribute is the baseline of the virtual Z axis (3D axis), but according to the official documentation it's not the only part. Then, translationZ will add extra distance to the surface and it's mainly used for animations.