Display ui time with customize time location (#7792)

* display ui time with customize time location

* fix lint

* rename UILocation to DefaultUILocation

* move time related functions to modules/timeutil

* fix tests

* fix tests

* fix build

* fix swagger

modules/timeutil/language.go

@@ -0,0 +1,36 @@
+// Copyright 2019 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package timeutil
+
+import (
+	"time"
+
+	"code.gitea.io/gitea/modules/setting"
+)
+
+var (
+	langTimeFormats = map[string]string{
+		"zh-CN": "2006年01月02日 15时04分05秒",
+		"en-US": time.RFC1123,
+		"lv-LV": "02.01.2006. 15:04:05",
+	}
+)
+
+// GetLangTimeFormat represents the default time format for the language
+func GetLangTimeFormat(lang string) string {
+	return langTimeFormats[lang]
+}
+
+// GetTimeFormat represents the
+func GetTimeFormat(lang string) string {
+	if setting.TimeFormat == "" {
+		format := GetLangTimeFormat(lang)
+		if format == "" {
+			format = time.RFC1123
+		}
+		return format
+	}
+	return setting.TimeFormat
+}