[3 - 5] Suggest on dashboard next section for the user to tackle

[caioertai]

• [X] Associate users with section
• [ ] Check acts_as_list gem for section ordering.
• [X] Might need to scope it with chapter for ordering
• [X] Check uncompleted sections from user (through :quizes, check left joins query) Section.all - User.completed_sections.
• [X] Display link for first few from the list.
• [X] Limit section list max-width for a percentage or something.