Updates to sel4webserver from camkes-3.7.x to camkes-3.8.0

• Created sel4webserver project containing an seL4 webserver application. Its purpose is to be a reference for implementing applications on seL4.
  • This project currently builds an odroid-xu4 VM that runs linux and gets some devices passed through to it.
• Add lighttpd module. This module will build and install a static binary of the lighttpd webserver into a VM overlay. It is currently configured to serve a static site on port 3000 out of /run/site in the VM.
• Add docsite package that downloads, builds and packages a docs.sel4.systems static website. It is intended for being served by the lighttpd webserver added previously.