CImg and WxCam: New Packages

In this commit, I'm including two softwares:
* CImg: A small, simple image toolkit library
* WxCam: a small, simple, wxGTK-based webcam application

>> +  buildInputs = with stdenv.lib;
>> +  [ unzip ];
>> +
>> +  builder = ./builder.sh;
>> +  
>> +  meta = {
>> +    description = "A small, open source, C++ toolkit for image processing";
>> +    homepage = http://cimg.sourceforge.net/;
>> +    license = cecill-c;
>
>Yes, the license is in stdenv.lib! Line 80 of lib/licenses.nix.

But this line seems to be out of scope where stdenv.lib.licenses is 
visible.