Added additional menu in <LayerEditor/>

This is to make the following options accessible to keyboard users

 - reorder layers
 - duplicate layer
 - delete layer
 - hide/show layer

package.json

@@ -30,6 +30,7 @@
     "github-api": "^3.0.0",
     "jsonlint": "github:josdejong/jsonlint#85a19d7",
     "lodash.capitalize": "^4.2.1",
+    "lodash.clamp": "^4.0.3",
     "lodash.clonedeep": "^4.5.0",
     "lodash.isequal": "^4.5.0",
     "lodash.throttle": "^4.1.1",
@@ -42,6 +43,7 @@
     "prop-types": "^15.6.0",
     "react": "^16.3.2",
     "react-addons-pure-render-mixin": "^15.6.2",
+    "react-aria-menubutton": "^5.1.1",
     "react-aria-modal": "^2.12.1",
     "react-autocomplete": "^1.7.2",
     "react-codemirror2": "^4.2.1",