Bug 1096330 - [Messages][RTL] Correctly handle recipient pills. r=julien

So here I see only two options to resolve RTL issue:

1. Alter ```.recipient``` template inside index.html and instead of ```<span .....>{name}</span>``` use ```<span .....><bdi>{name}</bdi></span>```. In such case we don't need to change any margin styles, but it's much risky because we have to made js changes to support new recipient element structure (currently edited recipient pill uses the same template);

2. Current option, apply ```dir="auto"``` to recipient template, but in this case we should override margins, because for ```-moz-margin-end``` is different for ltr and rtl contact.  

I chose 2nd option as it's both less invasive and less risky, but let me know what you think.