Support additional weekly resource attachments

[fabnemEPFL]

Adds reusable support for extra weekly attachments using numbered frontmatter pairs:

resource_1_label: "Mock quiz (PDF)"
resource_1_file: "resources/week-02-mock-quiz.pdf"
resource_2_label: "Worked example (PDF)"
resource_2_file: "resources/week-02-worked-example.pdf"

This PR is stacked on PR #47 so the Week 2 student notes and slides/BiGHT-W2.pdf are reviewed only there. This PR also renames the Week 2 content file to match the new Week 2 title.