Remove element from a dataset

Refs https://redmine.teklia.com/issues/3653
Depends backend#1609 (closed)

A user should be able to remove an element from an open dataset:

• from the list of datasets where the element is in use (details panel). A small delete icon should be visible, triggering a confirmation modal before actually deleting the element
• from the list of elements in a dataset. A small delete icon should be visible, triggering a confirmation modal before actually deleting the element

Do not bother hiding the icon if the dataset is not open, the backend will provide an explicit error message, and this feature is important BUT rarely used.