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

src/styles/_layer.scss

@@ -50,14 +50,25 @@
     @include flex-row;
   }
 
-  &-icon-action svg {
-    fill: $color-black;
+  &-icon-action {
+    display: none;
+
+    svg {
+      fill: $color-black;
+    }
   }
 
   .maputnik-layer-list-item:hover,
   .maputnik-layer-list-item-selected {
     background-color: lighten($color-black, 2);
 
+    .maputnik-layer-list-icon-action {
+      display: block;
+      background: initial;
+      border: none;
+      padding: 0 2px;
+    }
+
     .maputnik-layer-list-icon-action svg {
       fill: darken($color-lowgray, 0.5);
 
@@ -168,3 +179,38 @@
     color: $color-lowgray;
   }
 }
+
+.more-menu {
+  position: relative;
+
+  &__button {
+  }
+
+  &__menu {
+    position: absolute;
+    z-index: 9999;
+    background: $color-black;
+    border: solid 1px $color-midgray;
+    right: 0;
+    min-width: 120px;
+  }
+
+  &__menu__item {
+    padding: 4px;
+  }
+}
+
+.layer-header {
+  display: flex;
+  padding: 6px;
+  background: $color-black;
+  border-bottom: solid 1px $color-midgray;
+
+  &__title {
+    flex: 1;
+  }
+
+  &__info {
+    min-width: 28px;
+  }
+}