Adds fitEllipseDirect to imgproc: The Direct least square (Direct) method by Fitzgibbon1999.

New Tests are included for the methods.
fitEllipseAMS Tests
fitEllipseDirect Tests

Comparative examples are added to fitEllipse.cpp in Samples.

New p3p algorithm (accepted by CVPR 2017) (#8301)

* add p3p source code

* indent 4

* update publication info

* fix filename

* interface done

* plug in done, test needed

* debugging

* for test

* a working version

* clean p3p code

* test

* test

* fix warning, blank line

* apply patch from @catree

* add reference info

* namespace, indent 4

* static solveQuartic

* put small functions to anonymous namespace

Remove useless backslash.

Add bib reference for overall hitrate and false alarm rate for the train cascade user guide (OpenCV 2.4).

Extension of the camera distortion model for tilted image sensors (Scheimpflug condition) including test

- fixed one BiB record
- moved algorithms overview to separate page
- added docs for some enumerations
- fixed some small documentation errors

- disabled doxygen tree
- enabled doxygen enum listing
- added imgproc reference to main page
- enabled BiB support
- chenged doxygen root page format