The result of the spike at T131314#2250027 (Review Icon support to see if it will benefit from ResourceLoaderImageModule):
> The extension uses only two icons - cog and horn.
>
> The benefits over the current implementation are:
>
> No need to keep the generated PNGs around, RL will generate them on the fly;
> Standard mw-ui-icon, rather than the current custom styled icon.
> Future potential benefits are:
>
> Specify different images for RTL and LTR languages if we want to do so;
> Multi-colored images based on the single SVG.
**Acceptance criteria:**
[] Switch the cog icon implementations to use ResourceLoaderImageModule and remove the css rule for .mwe-popups-settings
[] Remove the unnecessary png.
== Test Plan
# Enable Page Previews
# Visit any page
# Dwell on a link for long enough that a preview appears
# Observe that the settings cog is visible
# Tap the settings cog and get taken to the preferences page (or the settings modal if you're logged out)