Moved accessibilityType to SSKeychainQuery.

This is to break the dependency of SSKeychainQuery on SSKeychain, so that the SSKeychainQuery can be used on its own.  It also allows those that use SSKeychainQuery on its own to specify accessibilityType on each query independently without having to change a static variable.

Also removed some redundant redefinitions of Security dictionary keys.
Added method for fetching attributes of security items (the previous behavior of fetchAll:) and updated fetchAll: to return the password data of any matching items.