Profile Cover 3.0.0

Notable Changes:
* Support cover gallery
* Fixed javascript access error property
* Changed permission `Upload/modify cover by self` to `Maximum upload cover images`
* Moved option default cover image to style property.
* Added style property to show avatar into cover block.

* Fixed user can remove cover by anyone even did not have permission
* Fixed less parser error in some cases
* [New] Automatically remove cover when user did not have permission to upload. This feature can be turn off through option.

* Fixed cannot remove cover
* Fixed missing covers when upgrade to 1.0.1
* Fixed undefined callback error

* Fixed cover not working in some cases.
* Improvement cover reposition
* Improvement add-on