Take place and not needed on all servers

- add lz4, diffutils, sed
- Setup basic seblu.net config files

- use https url, inside a variable
- forbit invalid pkgname
- doesn't use .sign as they are not supported by makepkg
- upstream patches (rc, stable) are no more prefixed by linux- before downloading
- upstream patches are symlinked instead of copied

svn not needed since I moved configs to git