Editing properties easier

[Miriam]

In order to work more effectively with a property, the editing process needs to be redone.
Deleting a property should directly delete it ( make it disappear from the list), and also editing properties needs to be easier--> meaning there should be a possibility to save property changing in between ( an apply button).

[Tobias Schlauch (tobias-schlauch)]

The apply button is already there. New properties are directly deleted. Exisiting properties are not directly deleted as this enables the revert functionality.

However you can just delete, revert, and clear values for single properties. These actions should also be usable in case of multiple selection.

[Tobias Schlauch (tobias-schlauch)]

In addition, the content of all cells can now be copied into the clipboard. The property dialog is non-modal and for each item a separate dialog can be shown.