Add "divider" and "divider_color" to order item options

[elchininet]

This pull request adds two new options in the order items.

Order Items Properties

Property	Type	Required	Description
divider	Boolean	no	Adds a divider line below the item
divider_color*	String	no	Sets the color of the divider line below the item (it overrides the root divider_color option)

* These options allow JavaScript or Jinja templates.

Screenshot

title: Custom Title
order:
  ...  
  - new_item: true
    item: Integrations
    href: /config/integrations
    icon: 'mdi:puzzle'
    order: 2
    divider: true
  ...

[coveralls]

coverage: 100.0%. remained the same
when pulling 40b1eb7 on add_divider_and_divider_color_to_items
into 107cccd on master.