Adding Arabic translation

I finished the Arabic translation of brackets, and i wanted just to inform you that i pulled the change on 'arabic-lang' branch.

As you may know, Arabic is read from RTL (Right-To-Left) like Hebrew, i followed a topic that was discussing this matter on Google Groups.

https://groups.google.com/d/topic/brackets-dev/R9lpXQN02wk/discussion

I noticed that the RTL will be supported in the next release of CodeMirror v3. until then, here is the Arabic translation, feel free if you want to integrate it to the build now or maybe in the next release (there is some display issues, but it's readable and comprehensible).

If you have any remarks, feel free to discuss.