rP18487 Introduced that the "deletable"-button is not enabled when there is no entity to delete by checking for the "delete" command and whether the entity state is undeletable. rP18773 Fixed multiple entities selected by introducing the same check as performed in `unit_actions.js`.
This patch introduces an optional `enabled`-element in the object returned to `selection_panels.js`, both removing hardcoding of "delete" and allowing other commands to specify whether the button ought to be enabled or disabled (e.g. unloading not allowed when the garrison holder is moving).