This change is needed to satisfy the increased memory usage of the dde_ipxe nic_drv. Issue #2121.
The functionality of the former "CAP" and "SIGNAL" services is now provided by core's "PD" service.
This patch changes the top-level directory layout as a preparatory step for improving the tools for managing 3rd-party source codes. The rationale is described in the issue referenced below. Issue #1082