Old title: "Allow units without Health component and use it for relics", and summary:
As mentioned in rP19345, it should be possible to have units without a Health component.
This is in particular relevant for units which are supposed to be indestructable, so having healthpoints if they can never change would be pointless.
The diff moves the Undeletable property from Health to Identity, because it should be possible to mark entities as undeletable without Health component too.
The SetUndeletable method was deleted, because changing template properties is not well supported with AIs (the change would have to be pulled and hardcoded through the GUIInterface).
(For the same reason a template approach was favored for D104.)
The treasure seeker woman on survival is marked as undeletable with a new special filter template (refs #2951, D215).
(This special filter template will be renamed to indestructable and extended to remove the DamageReceiver component once we fix the AI for D230)
The updatePanelEntityHealthBar needs an early return and in the same turn removes some pointless unused option to show the Health point bar vertically or inverted horizontally.
(The player might expect the capture bar in the top panel, refs D289, but out of scope).
The undeletable property was added to Health in rP17408 fixing #3590 (https://github.com/0ad/0ad/commit/55cfb72a3231b3058063b13975c75e4e9f2aa2fb)