feat: add backspace and caps lock icons (#803)

Summary:
- svg sprite generate with xmlns:xlink="http://www.w3.org/1999/xlink" namespace
- uhk-icon-agent-icon css class renamed to uhk-icon-pure-agent-icon because
  it collided with agent icon sprites
- added backspace and caps lock icons

packages/uhk-web/src/app/components/side-menu/side-menu.component.html

@@ -131,7 +131,7 @@
     </li>
     <li class="sidebar__level-0--item" [routerLinkActive]="['active']">
         <div class="sidebar__level-0">
-            <i class="uhk-icon uhk-icon-agent-icon"></i> Agent
+            <i class="uhk-icon uhk-icon-pure-agent-icon"></i> Agent
             <i class="fa fa-chevron-up pull-right"
                (click)="toggleHide($event, 'agent')"></i>
         </div>