3.2.0-rc

(2.4) Backports from master branch (#7854)

To resolve undefined "Mat_to_vector_KeyPoint" error

improved fix for java wrapper generator (gen_java.py) to avoid generation of java methods with duplicate signatures(v3)

Before:
    Ptr<Dictionary>((cv::aruco::Dictionary*)dictionary_nativeObj)
After:
    Ptr<cv::aruco::Dictionary>((cv::aruco::Dictionary*)dictionary_nativeObj)

* fix for feature2d java wrappers as described in this post: http://answers.opencv.org/question/101675/surfsift-java-wrapper-for-opencv-3xosx-1011/

* fix for feature2d java wrappers as described in this post: http://answers.opencv.org/question/101675/surfsift-java-wrapper-for-opencv-3xosx-1011/

* rollback of one change as requested (similar change already merged)

While generating Java JNI wrappers package names with an underscore (`_`) character where not properly escaped according to https://docs.oracle.com/javase/8/docs/technotes/guides/jni/spec/design.html#resolving_native_method_names (see also: https://github.com/Itseez/opencv_contrib/issues/652).

This fix replaces all the occurrences of `_` with `_1` resulting in proper JNI method names.

They were issued for every frame retrieved - even in a release build.

* Adds the main features2d header to the parse list for the generator.
* Removes the manual definition of drawKeypoints and drawMatches since these are now included in the main header.
* Updates the generator to ignore SimpleBlobDetector, FlannBasedMatcher and DescriptorMatcher as these cause conflicts with the generator. This is okay since these were not previously included in the distribution anyway, so no harm is done.

 - cv2.UMat implemented - python thin wrapper for UMat
 - no implicit copy from GPU to Host done, resulting UMat can be passed to next function without overhead
 - cv2.UMat.get() - to fetch data to Host
 - new tests covers: ORB, BFMatcher, goodFeaturesToTrack, calcOpticalFlowPyrLK

refactored; added Camera2, notify callbacks, front/back maxCamera sizes; disable new stuff if target API < 21

Corrected typo and unused imports

a simple sample will look like:

```java
public class MainActivity extends Activity implements CameraGLSurfaceView.CameraTextureListener {

	CameraGLSurfaceView mView;
	ByteBuffer buf;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
                WindowManager.LayoutParams.FLAG_FULLSCREEN);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON,
                WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
        setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_LANDSCAPE);

        mView = new CameraGLSurfaceView(this, null);
        mView.setCameraTextureListener(this);
        setContentView(mView);
        buf = ByteBuffer.allocateDirect(1920*1080*4);
    }

    @Override
    protected void onPause() {
        mView.onPause();
        super.onPause();
    }

    @Override
    protected void onResume() {
        super.onResume();
        mView.onResume();
    }

	@Override
	public void onCameraViewStarted(int width, int height) {
		// TODO Auto-generated method stub

	}

	@Override
	public void onCameraViewStopped() {
		// TODO Auto-generated method stub

	}

	@Override
	public boolean onCameraFrame(int texIn, int texOut, int width, int height) {
		Log.i("MAIN", "onCameraFrame");
		int w=width, h=height;
		/*
		// option 1:
		// just return 'false' to display texIn on screen
		retutn false;
		*/

		/*
		// option 2:
		// fast copy texIn to texOut
		GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
    	GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, texOut);
		GLES20.glCopyTexImage2D(GLES20.GL_TEXTURE_2D, 0, GLES20.GL_RGBA, 0, 0, w, h, 0);
		return true;
		*/

		// option 3:
		// read, modify and write back pixels
		GLES20.glReadPixels(0, 0, w, h, GLES20.GL_RGBA, GLES20.GL_UNSIGNED_BYTE, buf);

		buf.rewind();
		// red line
		for(int i=0; i<h; i++) {
			buf.position(w*4*i+i*4);
			buf.put((byte) -1);
			buf.position(w*4*i+i*4+4);
			buf.put((byte) -1);
		}
		buf.rewind();

		GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
    	GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, texOut);
		GLES20.glTexSubImage2D(GLES20.GL_TEXTURE_2D, 0, 0, 0, w, h, GLES20.GL_RGBA, GLES20.GL_UNSIGNED_BYTE, buf);
		return true;
	}
}
```

fixing fourcc

Android: renamed default library name for static and dynamic fallback load; fixed libz import for 64-bit platforms