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

@incuna/js Please merge, ta!
Cool, so that'll work for all future eDetails, but I like that using this with any other eDetail (which it will be, because the Chrome update is on all of our machines) doesn't have a Sass dependency.

The only advantage I see to moving these inline styles out-of-inline is so they can be styled, but their reason for existence isn't to be styled. They happen to inherit the text colour of the app so should be visible most of the time, however in circumstances when they are not I appreciate that a class to style would be useful so I'll add that. However I see a Sass dependency more of a crutch than an improvement.