[BLUEJ-928] Add function to initialise Git repository for current project

We now have Git support. Unlike SVN, Git doesn't need a remote repository to get started. You can just make a Git repository for the current files without a remote to push to. I think it would make sense to have a button (or an option under the Share button) in BlueJ to create an in-place Git repository for the current project.

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Issue metadata

• Issue type: Task
• Priority: Medium