Bt india

Ok, I have made some changes to this feature in order to DRY it up a bit and make it more efficient. There are no longer any repeated/copied snippets, and the changes made for the /custom/* routes do not affect the current routes. For proof of concept, pull down and navigate to /modern, and then /custom/modern in another tab. in an idea world we strip out all of those hardcoded declarations for /modern, /client-solutions, /legacy, etc.

I know several of the UI guys in London are out at the moment, but this is something I need to keep pushing forward with for LP India. Would love for @i-like-robots or @Ianfeather to take a look and let me know your thoughts.
`show_js` is a weird name in my opinion. Because it's never actually 'shown'. It's a small thing, but `include_js` would be more appropriate i think. Also, given that it's true 99% of the time, could it not just default to true and be overridden for noscript pages?