Enhanced cookie settings

We needed to control additional cookie attributes such as the domain and httpOnly flag. Hence the first few commits. Furthermore, our code was already using SessionCookieConfig from Servlet 3.0 to set these values, so I figured in the interest of making this plugin a "drop-in replacement" to add support for that too in the last commit. Note that because there's no clear time at which the values in SessionCookieConfig will have been set (we are doing it in Bootstrap.init), and in fact the values could change at any time, the lookup has to be done each time a cookie is created, rather than once at initialization time.