Map card: prevent adding several SAME items

[ildar170975]

It is possible to add same item several times:

  - type: map
    entities:
      - entity: device_tracker.demo_paulus
      - entity: device_tracker.demo_paulus
      - entity: device_tracker.demo_paulus

Suggestion: prevent adding SAME item.

"SAME" means "with same label_mode".
Imho these scenarios should be allowed:

  - type: map
    entities:
      - entity: device_tracker.demo_paulus
      - entity: device_tracker.demo_paulus
        label_mode: state
      - entity: device_tracker.demo_paulus
        label_mode: attribute
        attribute: battery