scid: New package, version 4.3.

Just saw Michael Raskin's GNU Chess and XBoard updates and did a short check if
Scid is already in nixpkgs. It wasn't, so I decided to add it, so thanks to
@7c6f434c :-)

The package involves a lot of patching, as usual with Tcl/Tk on NixOS. In this
case the program is written in C++ and embeds the Tcl/Wish interpreter.

Unfortunately this doesn't make it easier to inject TCLLIBPATH, as there doesn't
seem to be a direct library call (well in theory you could `lappend TCLLIBPATH`,
but that won't help with TK_LIBRARY).

Signed-off-by: aszlig <aszlig@redmoonstudios.org>