GitLab

As requirement of #2390 , removed multiphase from WebUI, document, and put all trials flatten on WebUI.

1. The major change is to split trial-jobs to trials in webui, and use parameter id as part of trial id.
2. If multiphase is enabled, the limitation of trial controls job count only, not trials actually.
3. When multiphase enabled, the trial status may not be right. Previous trials in a job will be marked as success, only last trial presents the job's status.
4. multiphase related documents and UX are removed.

minor changes,
1. Update dev document for webui development.