Move module loading to after initialization of QlRequest and QlResponse

In case QlSession::discard_get_sid_if_redundant() decides to redirect,
this avoids loading all the modules without then using them.
Move logic to detect requests for static files from QlCoreModule to QlRequest

Being a request for a static file is logically a property of QlRequest, so
move the detection code there, exposing the result as a method,
QlRequest::is_url_static_file().