Grouped habits / sub-habits

[alythobani]

Allow users to cluster related habits together, or break a habit into sub-habits. A habit will only be treated as completed if all of its sub-habits are completed.

for example
Morning Routine: [Brush and Floss, Vitamins, Meditate]

I don't see an issue with allowing them to be nested as well – e.g. you could have "Practice Guitar" split into "Scales" and "Songwriting", and have "Scales" be split up into "Minor Scales" and "Major Scales".