Add shell script dependencies + Fix installation bug + Revamp gnupaste/epfl-vpn

This commit adds the missing shell script dependencies to the Readme and the Arch Linux PKGBUILD.

Also, for the Arch Linux PKGBUILD, the dependency array is moved into the package() function. This is because makepkg considers packages in the global depends array as buildtime dependencies, too, whereas it does not provide any means to declare runtime-only dependencies. This is a commonly used "hack" to work around that limitation (see this).

Moreover, the PKGBUILD mistakenly installed velo.pl as tl.pl, thus erasing the real tl.pl; this is fixed now.

Finally, I was so keen to (slightly) revamp the gnupaste and epfl-vpn scripts (for latter, the options are changed now, so backwards compatibility is broken there).