[ONOS-3642] Add GUI Meter View

This implements the web GUI meter view.
Current implementation uses the group table icon for meter,
and the revised meter icon will be updated in following commit.
See ONOS-3645 for detail.

Change-Id: Iaa2e673ef83024135d757a2aaec1c31a87263217
diff --git a/web/gui/src/main/webapp/app/view/flow/flow.html b/web/gui/src/main/webapp/app/view/flow/flow.html
index f7142d3..374da0b 100644
--- a/web/gui/src/main/webapp/app/view/flow/flow.html
+++ b/web/gui/src/main/webapp/app/view/flow/flow.html
@@ -30,6 +30,11 @@
                  icon icon-id="groupTable" icon-size="36"
                  tooltip tt-msg="groupTip"
                  ng-click="nav('group')"></div>
+
+            <div class="active"
+                 icon icon-id="meterTable" icon-size="36"
+                 tooltip tt-msg="meterTip"
+                 ng-click="nav('meter')"></div>
         </div>
     </div>