Modified variable name to be returned in EnvironmentPage.scala

Modified typos in EnvironmentPage.scala

Removed Top level json field name in EnvironmentPage.scala
Added spaces at the place where creating json in ExecutorPage.scala
Simplified json creating logic in JobProgressPage.scala
Simplified PoolPage.scala
Simplified json creating logic in StagePage.scala
Simplified json creating logic in RDDPage.scala
Simplified json creating logic in StoragePage.scala
Modified variable name in StagePage.scala