Add layers control options support

Example call

    $scope.leaflet = 
      center:
        lat: 59.95
        lng: 30.3
        zoom: 10
      layers:
        options:
          collapsed: false
        baselayers:
          osm:
            name: 'OpenStreetMap'
            url: 'http://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png'
            type: 'xyz'
Update layers.js
Merge pull request #271 from pomahtuk/patch-2

Add layers control options support