rest-gen/JavaScript: Automatically initialize cookie jar for node.js users

[mb21]

Update base.js to produce something like in this latest commit.

This doesn't force the consumer of the silk module (like example.js) to require request if he wants to run with the default config.

[bergmark]

To clarify this, currently when using the generated JS client on node.js you need to initialize a cookie jar manually like this if you want cookie handling:

Api.defaultAjaxOptions.jar = require("request").jar();

This should be done inside base.js instead, and not globally. Each Api instance should get its own cookie jar.

[bergmark]

This has been fixed!