use JsonSerializable
Allow Collection::sortBy and sortByDesc to accept a string
Added Config::append method.
Move Config::append to helper instead.
Missed closing bracket.
Merge pull request #3228 from anlutro-pull-requests/jsonserialize

[4.2] Implement JsonSerializable
Fix comments.
Merge pull request #3284 from Anahkiasen/collection-sortby

Allow Collection::sortBy and sortByDesc to accept a string
Update change log and code.
Added sum method to collection.
Merge branch '4.1'