Add a .gitignore file to the repository

As of now, there is no .gitignore file included in the repository. This could lead to unintentionally committing the test or production database and/or the compiled target to the server when using git add -A. As the repository remains private (I am assuming this project is not Open Source) it is not primarily a security concern. The initial .gitignore file I would propose is included in this pull request.