Ensure IE caches CMS resources correctly

Now that we got rid of the war overlays for cms xinha and skin modules, we need to make sure there is no regression wrt CMS7-4194, because the fix that solved that is no longer included.

According to http://support.microsoft.com/kb/234067 we need to make sure that we send proper headers. We should send both expires (http 1.0) and cache-control (http 1.1) headers with the correct values.

Currently the resource servlet does not do that in all cases: if the configured cache time out is 0 or less those headers are not sent. We need to set those headers in that case as well.

We might also specify default cache timeouts for resources in the archetype.