### What changes were proposed in this pull request?
1, add a basic doc for executor page
2, btw, move the version number in the document of SQL page outside
### Why are the changes needed?
Spark web UIs are being used to monitor the status and resource consumption of your Spark applications and clusters. However, we do not have the corresponding document. It is hard for end users to use and understand them.
### Does this PR introduce any user-facing change?
yes, the doc is changed
### How was this patch tested?
locally build
<img width="468" alt="图片" src="https://user-images.githubusercontent.com/7322292/63758724-d2727980-c8ee-11e9-8380-cbae51453629.png">
Closes#25596 from zhengruifeng/doc_ui_exe.
Authored-by: zhengruifeng <ruifengz@foxmail.com>
Signed-off-by: Sean Owen <sean.owen@databricks.com>
