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/user/settings/organization.tmpl

@@ -22,7 +22,7 @@
 								<button type="submit" class="ui blue small button" name="uid" value="{{.ID}}">{{$.i18n.Tr "org.members.leave"}}</button>
 							</form>
 						</div>
-						<img class="ui mini image" src="{{.RelAvatarLink}}">
+						{{avatar . 28 "mini"}}
 						<div class="content">
 								<a href="{{.HomeLink}}">{{.Name}}</a>
 						</div>