Timeline feature preview
Move Timeline styles to default.css.
Move strings to lang files and use lang_get().
Move timeline api to core/timeline_api.php.
Remove todo from timeline_inc.php.
Add bug_history date modified index.
Added user date_created index for user creation events.
Add missing lang_get() to timeline_inc.php
Fix handling for disabled avatars.
Addressing misc timeline review comments.
Added handler and notes access checks for timeline events.
Remove timeline.valid() in favor of creation time validation.
Adjust copyright message.
Precache all timeline issues.
Remove index on user date created field since it is not necessary.
Revised the styles to work for avatar off/on modes.
Move timeline classes to core/classes.
Limit timeline to 50 events with more option.
Use constructs, move comparison to classes, tie break for equal timestamp.
Fix filtering logic when showing first N events.