Have interactive tutorials

This is for https://github.com/jquery/gsoc/wiki/GSoC-2016-Ideas-List#jquery-learning-center---interactive-tutorials-for-learn-and-other-sites

The "Interactive tutorials" project for the jQuery Learning Center should provide a full learning experience, with articles/lectures and a tutorial to test the acquired knowledge. The project should run on our current infrastructure and it should be completely integrated in the Learning Center website. The latter is a WordPress-based website.

Under the technology point of view, this means that the project should be based on PHP and MySQL for the back-end. In particular, to create a seamless experience, we favor the idea of creating the project as a WordPress plugin.

For what concern the front-end, in addition to HTML5, CSS, and JavaScript we want the project to be built using jQuery. As the jQuery Foundation we love our projects and we want to share our experience and expertise with the student. We don't dictate any methodology for the CSS code or any language that compiles to CSS, but the use of Sass and BEM is recommended. At this stage of the project we are only aiming to create a desktop experience, thus smartphones will be out of scope.

Our aim isn't to compete with Codecademy, Code Wars, Code School, or similar services. We want to create a better experience for the users that visit our learning center by providing them with some tests. These tests will help them in retaining the knowledge they acquire by reading our articles and tutorials and by watching our videos. For this reason, we aren't interested in any rank system or in storing users data.

Our idea is to store only the description, some hints, and the proposed solution for each test. A test can be either a question with some preset answers or a request to write some code. Hints should be only shown on user's request to give some guidance about the solution. The test should be placed at the bottom of each page containing the tutorial or the video, and should only be shown on user's request (e.g. by clicking a button).

Start with the linked GSoC proposal and the current jQuery Learning Center at learn.jquery.com to understand the existing WordPress infrastructure. Define the plugin scope and integration points before implementation; done should include on-demand tutorial tests with questions or code tasks, hints, and solutions, without user accounts, rankings, or stored user data.