Add first devtool: prev/next arrows for broken swiping in Chrome

@incuna/js Please merge, ta!
I don't see how testing against the prototype will make any difference: `MainRouter.prototype.setview` will still be as brittle as `MainRouter.setView`, no?

But yes, this is brittle and not great, but it works without having to tool the other libraries to match it.

The aim behind this line is to ensure we have something that is controlling the views and so `MainRouter.on('change:view')` will be captured.