Analysis task page is slow to load

Analysis task page is slow to load
https://bugs.webkit.org/show_bug.cgi?id=152517

Reviewed by Andreas Kling.

The slowness comes from r194130 which made the JSON API at /api/analysis-tasks to report the start
and the end of each analysis task. This query was adding ~2s to the total JSON generation time.

Cache these values on analysis_task table since they never change once an analysis task is created.

* init-database.sql: Added columns task_start_run_time and task_end_run_time to analysis_task table.
Also added the missing drop statements at the top.

* public/api/analysis-tasks.php:
(fetch_and_push_bugs_to_tasks): Don't fetch the latest commit time of the start and the end.
(format_task): Report task_start_run_time and task_end_run_time as startRunTime and endRunTime.

* public/privileged-api/create-analysis-task.php:
(main): Set start_run_time and end_run_time when creating an analysis task.
(time_for_run): Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@194611 268f45cc-cd09-0410-ab3c-d52691b4dbfc