checklists WIP
Tasks: add double-click to edit, and date-picker-popup for
due-dates. Show red dates when overdue (basic)
checklists: checklist as <li> instead of <label>, so that inline-editing
doesn't trigger checkmark. Unfortunately means we need to replicate some
bootstrap css
checklists: tmp commit to showcase how inline checklists look on
tasks (only for todos for comparison)
checklists: add inline-checklists user preference, and hide inlines when
editing