Do not require the current working directory to be a Git repository

[pbuyle]

One of the goal of the plug-in is to make as few as possible assumptions on the development workflow. There is no need for the current working to be a Git repository (any other VCS/SCM could be used, or none at all) but currently this is still an assumption made by the plugin as it try to backup/restore a .git directory and a .gitignore file.