[make] Build chroot directory.
Remove nodejs build folder.
[makefile] Remove chroot jail.
[makefile] Phony rmbuildroot
chroot: add user myself.
chroot: library to control the sandbox.

Includes copying data to it and running commands.
Ajax hook for shell commands (via chroot).
chroot: add programs.
chroot: remove readkey files when setting up sandbox
Jail update nit.
Set Content-Type appropriately.

Also ensures that plug=none requests get the latest version without causing a
write.
ScoutCamp upgrade.
New version to fix dependencies.
Chroot: save output files back in the file tree.
Sandbox shell: Erase all data in /tmp/ to avoid leaking.

That way, we avoid having both leaking information from a particular sandbox
shell run, and giving the possibility to flood the hard drive fast.
sandbox-shell: chmod files to chroot user