Fixes#2876 with @paulmelnikow's suggestion
Moved imports of `ServiceTester` and `createServiceTester` to a separate file so that dev dependencies are not imported by service classes.
Refs #2510
I'm going to delete or change some more logos in a further PR or two, but lets start off with the (hopefully) non-controversial ones. I think in all of these cases it is fairly clear-cut that we are not losing anything by removing our icon in favour of simple-icons now that we apply a sensible colour by default.
This reimplements the idea @bkdotcom came up with in #1519, and took a stab at in #1525. It’s a really powerful way to add all sorts of custom badges, particularly considering [tools like RunKit endpoints and Jupyter Kernel Gateway](https://github.com/badges/shields/issues/2259#issuecomment-444186589), not to mention all the other ways cloud functions can be deployed these days.
