Major Description
When running Spark with reverse proxy enabled, the query parameter of the request URL can be encoded twice: one from the browser and another one from the reverse proxy(e.g. Nginx).
In Spark's stage page, the URL of "/taskTable" contains query parameter order[0][dir]. After encoding twice, the query parameter becomes `order%255B0%255D%255Bdir%255D` and it will be decoded as `order%5B0%5D%5Bdir%5D` instead of `order[0][dir]`. As a result, there will be NullPointerException from https://github.com/apache/spark/blob/master/core/src/main/scala/org/apache/spark/status/api/v1/StagesResource.scala#L176
Other than that, the other parameter may not work as expected after encoded twice.
We should decode the query parameters and fix the problem
