Mobile Responsive Styles (#580)

* WIP: Responsive styles

* Flip breakpoints, ensure doc doesn't spread

* Add MenuIcon

* Refactor Sidebar to share mobile responsive styles

* Fix accidental find/replace

* Tweak padding to take into account icon spacing

app/stores/UiStore.js

@@ -10,6 +10,7 @@ class UiStore {
   @observable activeCollectionId: ?string;
   @observable progressBarVisible: boolean = false;
   @observable editMode: boolean = false;
+  @observable mobileSidebarVisible: boolean = false;
 
   /* Actions */
   @action
@@ -65,6 +66,16 @@ class UiStore {
   disableProgressBar() {
     this.progressBarVisible = false;
   }
+
+  @action
+  toggleMobileSidebar() {
+    this.mobileSidebarVisible = !this.mobileSidebarVisible;
+  }
+
+  @action
+  hideMobileSidebar() {
+    this.mobileSidebarVisible = false;
+  }
 }
 
 export default UiStore;