Using fake timestamp in OS version make some results invisible

Using fake timestamp in OS version make some results invisible
https://bugs.webkit.org/show_bug.cgi?id=152289

Reviewed by Stephanie Lewis.

Added commit_order column to explicitly order OS versions. This fixes the bug whereby which
baseline results reported with only OS versions are shown with x coordinate set to 10 years ago.

To migrate the existing database, run:
    ALTER TABLE commits ADD COLUMN commit_order integer;
    CREATE INDEX commit_order_index ON commits(commit_order);

Then for each repository $1,
    UPDATE commits SET (commit_time, commit_order) = (NULL, CAST(EXTRACT(epoch from commit_time) as integer))
    WHERE commit_repository = $1;

* init-database.sql: Added the column.
* public/api/commits.php:
(fetch_commits_between): Use commit_order to order commits when commit_time is missing.
* public/api/report-commits.php:
(main): Set commit_order.
* tools/pull-os-versions.py:
(OSBuildFetcher.fetch_and_report_new_builds):
(OSBuildFetcher._assign_order): Renamed from _assign_fake_timestamps. Set the order instead of a fake timestmap.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@194088 268f45cc-cd09-0410-ab3c-d52691b4dbfc