Add Arabic Translation

أهلا ومرحبا بكم - another is nearing the finish line! :) The Arabic translation is being reviewed and is nearly complete. Greetings to approximately 300 million Arabic-speaking people that can now learn more about Bitcoin in their native language.

Huge thanks to all of the translators, reviewers and coordinators that have assisted us with this!

Here's a link to the live preview:
http://bitcoinar.us.to/ar/