Clean up icons

Clean up duplicate svg icons from assets directory.
Created a statusIcon component to dynamically render
status icons instead of using background-image in
scss files.

- Moved/removed on, off, critical, warning svg icons from
  assets directory
- Updated background-image status icons to use <icon>
  or <status-icon> directive

Signed-off-by: Yoshie Muranaka <yoshiemuranaka@gmail.com>
Change-Id: Ic0f06d78b0861d6f60d40b2dcc0b80fd6dad2a88
diff --git a/app/configuration/controllers/network-controller.html b/app/configuration/controllers/network-controller.html
index 102f1f2..0ec143c 100644
--- a/app/configuration/controllers/network-controller.html
+++ b/app/configuration/controllers/network-controller.html
@@ -121,7 +121,7 @@
     <div class="screen-reader-offscreen modal-description">Change network settings</div>
     <!-- accessibility only; used for screen readers -->
     <div class="page-header">
-      <span class="icon icon__warning inline"><span class="accessible-text" role="alert">Warning</span></span>
+      <icon file="icon-warning" aria-hidden="true"></icon><span class="accessible-text" role="alert">Warning</span>
       <h3 class="modal-title inline">Change network settings</h3>
     </div>
     <div class="modal__content">