migrate from com.* to alternatives (#14103)

* remove github.com/unknwon/com from models

* dont use "com.ToStr()"

* replace "com.ToStr" with "fmt.Sprint" where its easy to do

* more refactor

* fix test

* just "proxy" Copy func for now

* as per @lunny

modules/util/copy.go

@@ -0,0 +1,20 @@
+// Copyright 2020 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 util
+
+import (
+	"github.com/unknwon/com"
+)
+
+// CopyFile copies file from source to target path.
+func CopyFile(src, dest string) error {
+	return com.Copy(src, dest)
+}
+
+// CopyDir copy files recursively from source to target directory.
+// It returns error when error occurs in underlying functions.
+func CopyDir(srcPath, destPath string) error {
+	return com.CopyDir(srcPath, destPath)
+}