Add to attachment and sub checklist to Planner Checklist

Hello,

I wish to add attachment to under Checklist. 

Because after i can't find relation easily between Checklist and attachment. 

Also With this abilities Checklist will be better:

1. Add Sub checklist under top level Checklist. This is for important for checking mini missions.

2. Assign employee to directly Checklist 

3. Add attachment to directly Checklist

4. Assign person as Supervisor , designer etc. Ability with can add roles with options is better to management.