* Use attr() instead of data() to prevent parsing of json

A fix for issue #2503 
Valid JSON text will be converted to a JSON object, not text , when using .data(). using .attr() prevents this behavior.

* Update gitbucket.js

Use different methods to get old and head values depending on the object type

* Document language missing
* Missing form label
* Image elements do not have [alt] attributes
* Fix metals specific configuration
* [user-scalable="no"] is used in the <meta name="viewport"> element or the [maximum-scale] attribute is less than 5
* Fix AvatarImageProviderSpec
* [id] attributes on active, focusable elements are not unique
* Links do not have a discernible name
* Links to cross-origin destinations are unsafe

- Cancel button didn’t work
- Redirection after remove didn’t work
- Diff wasn’t displayed at the remove confirmation page

Add extra mail address support.

http://stackoverflow.com/a/25674229

# Conflicts:
#	src/main/webapp/assets/common/js/gitbucket.js

Improvement experience speed
 * lazy diff rendering ( it is effective if tha diff has a lot of files ).
 * some feature implemented by javascript, to implement by css.
 * some javascript event handlers on each elements move to on parent elements.