Macaron: Strip down renderer middleware (#37627)

* strip down macaron renderer

* inline renderHTML

* remove IndentJSON parameter

* replace renderer with a html/template set

* fix failing test

* fix renderer paths in tests

* make template reloading even simpler

* unify ignored gzip path lookup

* fix csp middleware usage

pkg/api/avatar/avatar.go

@@ -118,7 +118,7 @@ func (a *CacheServer) Handler(ctx *models.ReqContext) {
 
 	if err := avatar.Encode(ctx.Resp); err != nil {
 		log.Warnf("avatar encode error: %v", err)
-		ctx.WriteHeader(500)
+		ctx.Resp.WriteHeader(500)
 	}
 }