treewide: vectorise iconography

Clear, crisp, resolution independent vector graphics replace the trusty
microscopic PNG. Some minor CSS changes were needed to constrain images
in some locations to make sure they don't consume too much space.

Iconography taken from Mate desktop theme with minor adjustments:

https://github.com/mate-desktop/mate-icon-theme/

Signed-off-by: Paul Donald <newtwen+github@gmail.com>

protocols/luci-proto-wireguard/htdocs/luci-static/resources/view/wireguard/status.js

@@ -128,7 +128,7 @@ return view.extend({
 					'click': ui.createHandlerFn(this, handleInterfaceDetails, ifaces[instanceName])
 				}, [
 					E('span', { 'class': 'ifacebadge' }, [
-						E('img', { 'src': L.resource('icons', 'tunnel.png') }),
+						E('img', { 'src': L.resource('icons', 'wireguard.svg'), 'style': 'width:32px;height:32px' }),
 						'\xa0',
 						instanceName
 					]),