Make Jetty timeouts configurable system wide

Our jetty container has several timeouts associated with it, and at least one of these is regularly getting in my way (the idle timeout after 120 sec). I tried setting a system property, with no effect and I've tried altering a jetty.xml found at solr-install/solr/server/etc/jetty.xml on all (50) machines and rebooting all servers only to have an exception with the old 120 sec timeout still show up. This ticket proposes that these values are by nature "Global System Timeouts" and should be made configurable in solr.xml (which may be difficult because they will be needed early in the boot sequence).