add option to display an entity value as an icon

It could be useful (and prettier) to display en entity value as its icon (e.g. battery levels). ## Old behavior (without PR) Configuration example: ```yml type: entities title: Capteurs de contact entities: - entity: binary_sensor.porte_cuisine_sous_sol type: custom:multiple-entity-row entities: - entity: sensor.porte_cuisine_sous_sol_battery name: false - entity: binary_sensor.porte_d_entree type: custom:multiple-entity-row entities: - entity: sensor.porte_d_entree_battery name: false ``` Screenshot:  ## New behavior (without PR) Configuration example: ```yml type: entities title: Capteurs de contact entities: - entity: binary_sensor.porte_cuisine_sous_sol type: custom:multiple-entity-row entities: - entity: sensor.porte_cuisine_sous_sol_battery name: false icon: true state_color: true - entity: binary_sensor.porte_d_entree type: custom:multiple-entity-row entities: - entity: sensor.porte_d_entree_battery name: false icon: true state_color: true ``` Screenshot: