Add a sample project to the development-seed.

Using `RAILS_ENV=development rake db:seed`, you can now generates a sample project: The project contains several issues, a timeline and lots of planning-elements to play with. Feel free to add some more sample data
to this pet-project.

The project is re-generated every time you seed the database, so every changes to the seeded project will be lost.

The ci is currently skipped, as travis currently does not run the seeding, so there is nothing to test there.