detect node-webkit and build with nw-gyp

The process here is as such
 - Recursively go up the path looking for package.json files.
 - When we find the last one, look to see if it has an engines setting, and if it does, look to see if it contains a setting for node-webkit
 - If there is a setting, we grab its version
 - If we have a node-webkit setting, skip the fetch (we can possibly fix this later?)
 - When building, choose between node-gyp and nw-gyp based on having found a node-webkit version
 - Set the target for nw-gyp configure to the version found earlier.