[lectures] add references in lecture detail

[TomasVotruba]

Take these:

• [x] https://github.com/pehapkari/pehapkari.cz/blob/master/source/_data/lecture_references.yml
• [x] and the one from https://docs.google.com/document/d/1MCnfFFWXxo262rebF1k-0W_-FbWVuj_3pc2WA3--UCM/edit?ouid=107371378567698701347&usp=docs_home&ths=true
• [x] and https://docs.google.com/forms/d/1M3hK--ZqKzaJ2peO84N3KNX26dmcBzWjSTzvZ8JB4k4/edit#responses

And put them automatically under each lecture like Tomas has: https://pehapkari.cz/kurz/ovladni-php-storm-od-zakladu-po-profi-tipy/

[TomasVotruba]

Close after adding all references