Add comments feature

[fedetask]

Adding comments with staticman. The staticman app is running on Heroku and pushes comments to this repo trough the GitHub account @campus-ai-app.

These points must be checked in order to approve:

• [x] Staticman configuration file staticman.yaml: configures how comments are inserted into the repo
• [x] Comment form: a form with name, email, and comment that performs a POST request to the staticman app with the appropriate data
• [x] Comment list: the list of comments in temporal order (latest first) for the given page
• [x] Configure staticman.yaml to push comments on master
• [x] Redirect user to same page after successful comment
• [x] Redirect user to same page with error if wrong input

Further improvements:

• [ ] Nested comments

[fedetask]

Actually the comment form already prevents a comment to be sent without a name or email