Social sharing buttons

[zarino]

Fixes #52.

Will need squashing / rebasing.

You can set which services appear in the list, via an admin settings page:

Then you can add the buttons as a "Widget" to any sidebar on the site:

Or to any post, using the "Share Buttons" block:

Here’s how they look in use:

[zarino]

@wrightmartin Apologies. Fixed now.

[wrightmartin]

ugh, whoops

This is merged https://github.com/mysociety/fixmyblock-wordpress/commit/5c9f44399e2e17705821055065be130bcb08153c