Add RTL styles

[andersevenrud]

I had this in v2 and should be back-ported. Basically add an attribute to the root element that sets all text CSS styles to RTL.

[andersevenrud]

@BoFFire I've started work on this. I've implemented everything into the client, so now I just have to go over the theme(s) and make some corrections to margins etc 🙂

[BoFFire]

Oh nice work @andersevenrud \o/ We appreciate. Thank you !

[andersevenrud]

I've also updated @osjs/panels and @osjs/gui now, so this should now work pretty well. The only things missing are:

• Icons with arrows needs to be swapped
• ContextMenu needs to be optimized a bit (when it appears outside the right viewport it's a bit wonky)
• Panes gui component resize event is inverted
• Some very minor theme style stuff

The language is detect by the first segment of a locale, ex: en_EN will be looked up as en in this table:

https://github.com/os-js/osjs-client/blob/master/src/config.js#L168

This will set an attribute in the DOM which the CSS handles.