performance tests for ORB

```
Geometric mean

                                           Name of Test                                              plain      ocl       ocl    
                                                                                                                           vs    
                                                                                                                         plain   
                                                                                                                       (x-factor)
ORB_Detect::OCL_ORBFixture::"img1.png"                                                               4.190 ms  5.488 ms     0.76   
ORB_Detect::OCL_ORBFixture::"stitching/a3.png"                                                       3.397 ms  4.680 ms     0.73   
ORB_Extract::OCL_ORBFixture::"img1.png"                                                              7.704 ms  52.499 ms    0.15   
ORB_Extract::OCL_ORBFixture::"stitching/a3.png"                                                      7.474 ms  52.478 ms    0.14   
ORB_Full::OCL_ORBFixture::"img1.png"                                                                 11.862 ms 56.656 ms    0.21   
ORB_Full::OCL_ORBFixture::"stitching/a3.png"                                                         10.876 ms 55.996 ms    0.19   
```