Merge pull request #8301 from tonyke1993:p3p_alg

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

doc/opencv.bib

@@ -897,3 +897,10 @@
   year={2010},
   publisher={Springer}
 }
+@INPROCEEDINGS{Ke17,
+  author = {Ke, Tong and Roumeliotis, Stergios},
+  title = {An Efficient Algebraic Solution to the Perspective-Three-Point Problem},
+  booktitle = {Computer Vision and Pattern Recognition (CVPR), 2017 IEEE Conference on},
+  year = {2017},
+  organization = {IEEE}
+}