Add URLs, harmonise formatting, and fix parse error in bibliography (#13228)

* Fixed parse error in bibliography

* Removed extra curly braces

* harmonized whitespace

* changed organisation -> publisher where appropriate. Organisation is intended as the author's organisation, not the publishing.

* harmonized capitalisation and whitespace

* Add links to about 1/3 of references

created from RAW memory buffers (without proper lifetime management)

- don't require "OPENCV_PYTHON{2,3}_INSTALL_PATH" if OPENCV_SKIP_PYTHON_LOADER=ON
- avoid unnecessary relative paths in generated config-X.Y.py

Reduce input size for OpenPose tests

introduced by commit 4e629000

  - add infrastructure support for Power9/VSX3
  - fix missing VSX flags on GCC4.9 and CLANG4(#13210, #13222)
  - fix disable VSX optimzation on GCC by using flag ENABLE_VSX
  - flag ENABLE_VSX is deprecated now, use CPU_BASELINE, CPU_DISPATCH instead
  - add VSX3 to arithmetic dispatchable flags