Moving documenation to mediawiki/selenium repository

See also https://gerrit.wikimedia.org/r/#/c/90535/

Change-Id: I69a3a109f2d2da476b0b2267fe90c81ae095b25e
Moving code used in multiple repositores to a Ruby gem

For more information see http://lists.wikimedia.org/pipermail/qa/2013-October/000509.html

Bug: 53579
Change-Id: I14d3a7f238295072da323000078c578eaab73466