Add ability to display and edit list elements

[nikku]

Is your feature request related to a problem? Please describe

In my form I'd like to have the ability to edit list elements.

Example: A list of invoices that are uploaded, a list of items to be double checked.

Describe the solution you'd like

• Be able to define a list element container that can hold arbitrary child elements as contents.
• List element container should have the ability to add or remove elements from the list (configurable)

Describe alternatives you've considered

People need to contribute list elements as custom components.

Additional context

Supported by form.io via the datagrid component.