re: assembla/#169 Second source field mapping dissapears

* includes/Config.php
  - added resource jquery.json

* includes/Forms/MetadataMappingForm.php
  - added ids to form tables

* resources/js/ext.gwtoolset.js
  - added logic to handle cookies in order to store/restore
    input/select fields added with js

Change-Id: I83c42f81df9b2fed0ad5e793d611e067b0ef3eb6
re: #169/assembla - Second source field mapping disappears

*addressed feedback from mark traceur @see https://gerrit.wikimedia.org/r/#/c/90041/2

Change-Id: I1bcd11f10d1441a10237a9b0e5d33c4f0f32c729