jquery.json is deprecated

 * use "json" instead as suggested
   https://www.mediawiki.org/wiki/ResourceLoader/Default_modules#jquery.json

Change-Id: Ib37dc3efc09b61264e462404b0befae43d93a734
Switch to JSON.(parse|stringify)

 * As suggested in,
   https://www.mediawiki.org/w/index.php?title=ResourceLoader%2FDefault_modules&diff=1217242&oldid=1199051

 * Should have been part of change,
   Ib37dc3efc09b61264e462404b0befae43d93a734

Change-Id: I354375a9a32a5ce379aca19b2d7c4c4114748c72
Remove jstorage.js fork

 * Use the one already available from core.

Change-Id: I0a985d20859529338b7bc83a5f40a949dfd00202