Add cookie support

[hstaudacher]

Currently their is no easy way to set cookies for a request. Maybe we should extend the @httptest Annotation to take some cookies.

[drejc]

Additionally there should be an option to dynamically set cookies / request headers
As currently headers can be only set via the @Header annotation which accepts only constant expressions.

Sometimes cookies / headers need to be set at test runtime (for instance a session cookie which is retrieved before the test is stared) in the @before method call.

[andreasmihm]

the cookies are transported in a header named Cookie, so I use restfuse and transport cookies by just adding a Header with the name "Cookie" and the value "MyCookieName=MyCookieValue"