Integrate ports into the main tree as a submodule.
A stripped down version of hsct.sh is added to tools, and Makefiles
gain new targets that implement part of hsct's prior functionality.
This arrangement improves usability and maintainability of ports,
reduces the likelihood of ports being broken by mainline changes,
and partially solves the issue with build logic being duplicated
in multiple places.
It is newly possible to build individual ports using make ports-NAME,
and all ports using make ports-all. This also installs the outputs to
uspace/dist, so ideally, simple make ports-all && make would create
an image with all ports included. This currently doesn't work only
because some ports fail to build.
