taskbar 6.x-1.0-beta4

- Allow tacore activity created time to be overriden
- Issue #1220150 by jcisio: Migrate Appbar alert into Taskbar Activity tacore
- Avoid fatal error if callback is not available.
- #1216638 - Allow sub-modules define hooks in separate files
- Wrong colspan value.
- Use taskbar-item-loading class name instead of loading.
- Issue #1234262 by jcisio: Fixed Taskbar should not refresh if unnecessary.
- Issue #1230954 by thehong, jcisio: Ajax refresh rate per item.
- Issue #1235020 by jcisio: Added Item can have more action than a status and an extra data.
- Issue #1234264 by jcisio: Added Support for optional long polling instead of periodical refresh.