added package for pipelight

Hi,

I created a package for Piplight (http://pipelight.net/cms/about.html). This one wasn't easy to package. Here are some thoughts and questions I had during the creation of the package.

 * Pipelight needs a number of patches to the current wine version. Thankfully Nix makes this easy because of the great `overrideDerivation` function.

 * Pipelight uses a lot of shell scripts which refer to programs by the full path. I patched these paths to contain just the filename of the executable (I don't know if this is the best approach).

 * I had problems when I tried to use the `$out` variable in `configureFlags`, so I overwrote the `configurePhase`. Is there a corresponding Nix variable for `$out` or another trick to get this to work?

 * Pipelight needs to download some files during usage. I replaced the downloader choices wget and fetch by curl since curl comes preinstalled on every NixOS installation. Is there a more flexible solution for downloading files?

 *  Pipelight lets you install proprietary browser plugins like MS Silverlight. During the enabling of those plugins you have to accept the corresponding licenses. Pipelight itself is free and open source. Do I have to set the `unfree` flag in the meta information?

I'm open for suggestions.

Best,
Sven