Add Rubyric exercises, details about the configuration of the exercises and instructions about local development

[jaguarfi]

Description

Instructions about testing Rubyric in a local environment is added. In addition, one more Rubyric exercise is added to the manual along with some detail about some of the configuration parameters.

Testing

I tested the exercises in http://localhost:8000/def/current/rubyric/example/

Is it Done?

Clean up your git commit history before submitting the pull request!

• [ ] I (developer) have created unit tests and the tests pass
• [ ] I (developer) have created functional tests (Selenium tests) if applicable
• [X] I (developer) have tested the changes manually
• [ ] Reviewer has finished the code review
• [ ] After the review, the developer has made changes accordingly
• [ ] Customer/Teacher has accepted the implementation of the feature

[jaguarfi]

This PR had something weird in it, and it added some other commits belonging to Jaakko and Saara. Anycase, now the PR is clean :)

[jaguarfi]

I think the instruction on how to configure Rubyric using the submit directive is lacking. However, the intention of this PR is to add another Rubyric example using the conf.yaml so that the users can at least copy and paste a working example of the Rubyric exercises, and follow the instruction presented in the Rubyric module to configure Rubyric. The second purpose of this PR was to add a brief description about how to test Rubyric locally and warn about the complexity of the process. That said, perhaps we could create a new issue to review the Rubyric module and add more guidance on how the different settings that may be included in the submit directive can affect the actual Rubyric exercise.