Direct avatar rendering (#13649)

* Direct avatar rendering

This adds new template helpers for avatar rendering which output image
elements with direct links to avatars which makes them cacheable by the
browsers.

This should be a major performance improvment for pages with many avatars.

* fix avatars of other user's profile pages

* fix top border on user avatar name

* uncircle avatars

* remove old incomplete avatar selector

* use title attribute for name and add it back on blame

* minor refactor

* tweak comments

* fix url path join and adjust test to new result

* dedupe functions

templates/org/member/members.tmpl

@@ -8,7 +8,7 @@
 			{{ range .Members}}
 				<div class="item ui grid">
 					<div class="ui one wide column">
-						<img class="ui avatar" src="{{.SizedRelAvatarLink 48}}">
+						{{avatar . 48}}
 					</div>
 					<div class="ui three wide column">
 						<div class="meta"><a href="{{.HomeLink}}">{{.Name}}</a></div>