Adds initial support for OpenGL ES 3.0

This doesn't add much but it prepares the way for Open GL ES 3.0 features.

- Updated library properties to support Android 4.3 API 18
- Adds fields to `RajawaliRenderer` containing the OpenGL major and minor version numbers for the EGL surface
- Added code to `RajawaliRenderer#onSurfaceCreated(GL10, EGLConfig)` to determine the EGL surface version
- Adds public getter methods to `RajawaliRenderer` to retrieve the major and minor version numbers

Note that nothing else is needed here. Due to the backwards compatibility of OpenGL ES 3.0 with 2.0, in Android when you request a 2.0 version EGL surface, you are automatically given a 3.0 surface if the device supports it.