Share checklist functionality

[AndreySurzhan]

As a user, I would like to get the function to share my checklists with other users

That would allow me to get feature to share my checklists with other users for collaborative learning foreign words and languages

AC:

1. Icon with pop-over on side user, who share checklist
2. Modal on Share button click, on side user, who share checklist
3. Alert icon on side user, who accept checklist
4. Modal on Accept button click, on side user who accept checklist
5. Functionality and api call