DRY script/direction

The config file specifies both `'script'` and `'dir'` properties for each language.

However, the direction is a property of the **script**, not a property of the language.   Latin is **always** written left-to-right and Arabic is **always** written right-to-left.

It is therefore only necessary to specify the script for each language.  The direction can be calculated automatically.

This PR removes (i.e. ignores) `'dir'` in the config file, and instead calculates the direction from the script.