require opengles 2.0 in this project
added opengles 2.0 support in main activity java
added a new class GLRenderer
implement abstract class GLRenderer.java
added GLES20Renderer.java
remove drawer list view; add checboxes
change set content view back to the default, add redraw when dirty property
add .idea and build folder to git ignore file
resolved conflicts
resolved conflicts when merging opengl support and master