Thanks for this brilliant app. I am currently self-hosting in docker.

Please allow users to copy a card, including tasks. I use templates so this would be very helpful.

Thanks again.

Describe the bug
Remove notification settings option from 3-dots-button menu for Documents, Tasks and Calendar

To Reproduce
Steps to reproduce the behavior:

1. Click on 3-dots-button for documents
2. Check option which are available in tis menu

Screenshots
![Screen Shot 2020-11-26 at 11 21 44 PM](https://user-images.githubusercontent.com/22451567/101045425-8fd32e80-3580-11eb

It would be nice to have a function to export the elements to JSON.
Using this it should be easier to send the elements to ajax for example.

I think it would be a good idea to add something like "bottom header". For example, I want to add a button to add a new card or some information

The FilterWidget is capable of providing all information we need. To reduce the code and keep it more maintainable, we should migrate the backend of the StackWidget to this infrastructure.

Depends on #737.