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

modules/auth/sso/sspi_windows.go

@@ -168,7 +168,7 @@ func (s *SSPI) newUser(ctx *macaron.Context, username string, cfg *models.SSPICo
 		IsActive:                     cfg.AutoActivateUsers,
 		Language:                     cfg.DefaultLanguage,
 		UseCustomAvatar:              true,
-		Avatar:                       base.DefaultAvatarLink(),
+		Avatar:                       models.DefaultAvatarLink(),
 		EmailNotificationsPreference: models.EmailNotificationsDisabled,
 	}
 	if err := models.CreateUser(user); err != nil {