Reload button in Location bar per ExE Boss

A WebExtension which adds the reload button to the Firefox Location bar.

This makes it look the way it did in Firefox Australis (29 – 56).

To get rid of the reload button in the location bar, you need to drag it off the Navigation bar in the Customise view.

To fix the icon being too dark when using dark themes, you currently need to enable svg.context‑properties.content.enabled in about:config, because Mozilla (see also: SVGWG issue #348).