Splitted the user settings code into several files to be more maintainable (#3968)

* refactor setting router code

splitted up one huge router settings file into the smaller files
representing the actual page structure

* move code to subfolder

* rename functions

* renamed files

* add copyright information

routers/user/setting/main_test.go

@@ -0,0 +1,16 @@
+// Copyright 2018 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 setting
+
+import (
+	"path/filepath"
+	"testing"
+
+	"code.gitea.io/gitea/models"
+)
+
+func TestMain(m *testing.M) {
+	models.MainTest(m, filepath.Join("..", "..", ".."))
+}