[Group week view] Add prev/next buttons

• Add buttons to navigate to previous or next week
• Move date information from the head of the left card to the page title
• Change head of left card to Lessons

changed milestone to %1.0a0

added part::frontend prio::1 type::feature labels

marked the checklist item Add buttons to navigate to previous or next week as completed

marked the checklist item Change head of left card to Lessons as completed

marked the checklist item Move date information from the head of the left card to the page title as completed

mentioned in commit 89bbd515

mentioned in merge request !5 (merged)

closed via merge request !5 (merged)

mentioned in commit 09da0f4d