fix(checklists): Make checklist To-Do behavior more intuitive

Previously, all To-Do scoring was multiplied by the length of the checklist, including cron "reddening" and ultimate scoring. The checkboxes themselves only affected MP bonuses. Now, checklist tasks redden at the same rate as any other task, and the score multiplier only applies to checklist items that have actually been accomplished when the user concludes the overall To-Do.

Fixes HabitRPG/habitrpg#2327, HabitRPG/habitrpg#2405, and HabitRPG/habitrpg#2483.