Support static preview with social style

[paulmelnikow]

The social badges have typically included ?style=social. However staticPreview returns serviceData which does not support the style parameter. This makes it impossible to render a static preview for the social badges.

e.g.

shields/services/github/github-followers.service.js

Lines 32 to 36 in f8b0472

	staticPreview: {
	label: 'Follow',
	message: '150',
	// style: 'social',
	},

This also came up in #2473 where I was adding an Endpoint badge, and thinking we should make it possible for a developer to make a badge which defaults to a particular style.

I'm not totally convinced we should do that. In some ways it violates a user's expectation, which is that Shields will always default to flat. Should we also let the developer specify flat-square or for-the-badge? At the same time, these are custom badges, and it's useful to be able to include especially logos by default. Maybe it's okay, for custom badges.

[chris48s]

Given we've only got 6 social badges in the home page examples (out of some-hundred in total), I reckon static preview for social badges would be nice to have but its quite low priority.

[paulmelnikow]

It's true it's not so important to render it statically, though it would be nice to drop support for exampleUrl which adds complexity in BaseService and the frontend.