[SPARK-4984][CORE][WEBUI] Adding a pop-up containing the full job description when it is very long

In some case the job description will be very long, such as a long sql. refer to #3718
This PR add a pop-up for job description when it is long.

![image](https://cloud.githubusercontent.com/assets/7018048/5847400/c757cbbc-a207-11e4-891f-528821c2e68d.png)

![image](https://cloud.githubusercontent.com/assets/7018048/5847409/d434b2b4-a207-11e4-8813-03a74b43d766.png)

Author: wangfei <wangfei1@huawei.com>

Closes #3819 from scwf/popup-descrip-ui and squashes the following commits:

ba02b83 [wangfei] address comments
a7c5e7b [wangfei] spot that it's been truncated
fbf6162 [wangfei] Merge branch 'master' into popup-descrip-ui
0bca96d [wangfei] remove no use val
4b55c3b [wangfei] fix style issue
353c6f4 [wangfei] pop up the description of job with a styled read-only text form field

core/src/main/resources/org/apache/spark/ui/static/webui.css

@@ -121,6 +121,14 @@ pre {
   border: none;
 }
 
+.description-input {
+  overflow: hidden;
+  text-overflow: ellipsis;
+  width: 100%;
+  white-space: nowrap;
+  display: block;
+}
+
 .stacktrace-details {
   max-height: 300px;
   overflow-y: auto;

core/src/main/scala/org/apache/spark/ui/jobs/AllJobsPage.scala

@@ -64,7 +64,7 @@ private[ui] class AllJobsPage(parent: JobsTab) extends WebUIPage("") {
           {job.jobId} {job.jobGroup.map(id => s"($id)").getOrElse("")}
         </td>
         <td>
-          <div><em>{lastStageDescription}</em></div>
+          <span class="description-input" title={lastStageDescription}>{lastStageDescription}</span>
           <a href={detailUrl}>{lastStageName}</a>
         </td>
         <td sorttable_customkey={job.submissionTime.getOrElse(-1).toString}>

core/src/main/scala/org/apache/spark/ui/jobs/StageTable.scala

@@ -112,9 +112,8 @@ private[ui] class StageTableBase(
       stageData <- listener.stageIdToData.get((s.stageId, s.attemptId))
       desc <- stageData.description
     } yield {
-      <div><em>{desc}</em></div>
+      <span class="description-input" title={desc}>{desc}</span>
     }
-
     <div>{stageDesc.getOrElse("")} {killLink} {nameLink} {details}</div>
   }