Adds support for multiple Cookie Jars.

Previously, there was a single global cookie jar shared between all web pages.
Now, one can have separate cookie jars for different web pages.

Makes CookieJar a normal class, not a singleton.
Moves many public CookieJar methods to public slots.
Adds default cookie jar to Phantom.
Adds the CookieJar module that provides access to cookie jars in javascript.
Adds cookie jar module tests.

Usage:
var jar = require('cookiejar').create();
var webpage = require('webpage').create();
webpage.cookieJar = jar;
...
webpage.close();
jar.close();

JS API changes:
Webpage:
    var jar = page.cookieJar; -- assigns 'jar' the given webpage's cookie jar.
    page.cookiejar = jar; -- sets 'jar' as the given webpage's cookie jar.
CookieJar:
    var jar = require('cookiejar').create(path)
        creates a cookie jar with persistent storage at the given file path
        (path not mandatory).
    var cookies = jar.cookies; -- assign's 'jar' the list of cookies in the
        cookie jar.
    jar.cookies = [c1, c2]; -- sets the cookie jar's cookies as the ones in the
        list.
    jar.addCookie(cookie) -- adds cookie 'cookie' to the cookie jar.

https://github.com/ariya/phantomjs/issues/11417