make avatar lookup occur at image request (#10540)

speed up page generation by making avatar lookup occur at the browser
not at page generation

* Protect against evil email address ".."

* hash the complete email address

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-Authored-By: Lauris BH <lauris@nix.lv>

models/models.go

@@ -124,6 +124,7 @@ func init() {
 		new(OAuth2Grant),
 		new(Task),
 		new(LanguageStat),
+		new(EmailHash),
 	)
 
 	gonicNames := []string{"SSL", "UID"}