Support RTL the right way

[grappler]

@yoavf gave a talk on "Right To Left Languages Support – The Right Way"

In his talk he discourages the use of rtl.css but instead use style-rtl.css which would be a replacement for style.css instead of rtl.css which override the ltr styles with rtl styles.

There are a couple of reasons why this is better.

• RTL users do not have worse performance by having to load an extra file for their styles.
• The RTL file can be generated automatically without having manually to change the design.

The style-rtl.css can be generated using a node task. After installing it npm install -g rtlcss, the generation happens with rtlcss style.css style-rtl.css. This is similar to the tool used to generate the CSS from Sass in #1149.

https://yoav.blog/2017/06/22/right-to-left-in-wordpress-the-right-way/

[davidakennedy]

I'm going to leave this for now. We need to work through the automation/build process items before moving on this.