Added if condition, whether faces are detected or not, will help to keep program running for some images.
If imwrite used along with imshow, it may produce error for :  No faces found.Aborting.. in function 'fit' (Bad Argument).

Add AprilTag dictionaries to be able to detect AprilTag markers. Add ArUco and AprilTag 2 citations.

* android: fix build warnings

* build: fix warnings

with Ogre 1.11 OGRE_INCLUDE_DIRS has only one element and the '}'
corrupting the last include path becomes noticable.

- almost all functionality of this module is covered by OpenCV dnn module
- module build has been broken for the long time due strong conflict with OpenCV dnn module
- requires external tinydnn library
- there are no tests

- eliminated "float th = 1e-5f" magic value (replaced to explicit checks)
- eliminate manual memory allocation
- avoid out of range access (i == alls)

Add CV_OVERRIDE