LIVY-353. Web UI: Added link to Spark UI for Sessions running on Yarn

PR moved from old repo cloudera/livy#327

[LIVY-353](https://issues.cloudera.org/browse/LIVY-353)

Followup to cloudera/livy#319 adding a link to the Application Id that links to the Spark UI. The link is grabbed from session.appInfo.sparkUiUrl if it exists, otherwise no link is created.

Screenshots

With an appId without link (in this case before the UI is generated):
![no-link](https://cloud.githubusercontent.com/assets/13952758/25873597/0307dd40-34c4-11e7-9993-925cbf7c749b.png)
With an appId link:
![link](https://cloud.githubusercontent.com/assets/13952758/25873599/0454c69a-34c4-11e7-85d2-31ebe993c5a3.png)
What it links to:
![spark](https://cloud.githubusercontent.com/assets/13952758/25873602/05864318-34c4-11e7-8e2c-2222ef7f6116.png)

Author: Alex Bozarth <ajbozart@us.ibm.com>

Closes apache#4 from ajbozarth/ui-app-link.

Author: ajbozarth

Diff for: server/src/main/resources/com/cloudera/livy/server/ui/static/all-sessions.js

@@ -16,6 +16,15 @@
  * limitations under the License.
  */
 
+function appIdLink(session) {
+  var appUiUrl = session.appInfo.sparkUiUrl;
+  if (appUiUrl != null) {
+    return '<a href="' + appUiUrl + '">' + session.appId + "</a>";
+  } else {
+    return session.appId;
+  }
+}
+
 function tdWrap(str) {
   return "<td>" + str + "</td>";
 }
@@ -25,7 +34,7 @@ function loadSessionsTable(sessions) {
     $("#interactive-sessions .sessions-table-body").append(
       "<tr>" +
         tdWrap(session.id) +
-        tdWrap(session.appId) +
+        tdWrap(appIdLink(session)) +
         tdWrap(session.owner) +
         tdWrap(session.proxyUser) +
         tdWrap(session.kind) +
@@ -40,7 +49,7 @@ function loadBatchesTable(sessions) {
     $("#batches .sessions-table-body").append(
       "<tr>" +
         tdWrap(session.id) +
-        tdWrap(session.appId) +
+        tdWrap(appIdLink(session)) +
         tdWrap(session.state) +
        "</tr>"
     );

Diff for: server/src/main/resources/com/cloudera/livy/server/ui/static/batches-table.html

@@ -22,7 +22,13 @@ <h4 id="batches-header" class="sessions-template">Batch Sessions</h4>
   <thead class="sessions-table-head">
   <tr>
     <th>Batch Id</th>
-    <th>Application Id</th>
+    <th>
+      <span data-toggle="tooltip"
+            title="Spark Application Id for this session.
+            If available, links to Spark Application Web UI">
+        Application Id
+      </span>
+    </th>
     <th>
       <span data-toggle="tooltip"
             title="Session State (not_started, starting, idle, busy,

Diff for: server/src/main/resources/com/cloudera/livy/server/ui/static/sessions-table.html

@@ -22,7 +22,13 @@ <h4 id="interactive-sessions-header" class="sessions-template">Interactive Sessi
   <thead class="sessions-table-head">
   <tr>
     <th>Session Id</th>
-    <th>Application Id</th>
+    <th>
+      <span data-toggle="tooltip"
+            title="Spark Application Id for this session.
+            If available, links to Spark Application Web UI">
+        Application Id
+      </span>
+    </th>
     <th>
       <span data-toggle="tooltip" title="Remote user who submitted this session">
         Owner