Dropdown supports nesting

[icarusion]

Description

UI looks like this:

Additional context

An API might look like this:

const items = [
 [
  {
    label: 'label',
    icon: 'icon',
    items: [
      [
        {
           //...
        }
      ]
    ]
  }
 ]
]

[benjamincanac]

This will be implemented in #1289.