Version Control System Improvments

To help users to collaborate and use version control tools easily, Godot 3.2 introduced the version control system. The initial project to integrate VCS (Version Control System) into Godot was created in GSoC 2019 by ironicallySerious. It had been an excellent initial effort. However, there are still many things to improve. This project aims to improve the compatibility, usability and reliability of the VC system in godot and godot-git-plugin.