Look for patches and files in the same dir as json file

[hadess]

xdg-app-builder should look for the patches in the same directory as the json file passed in.

[alexlarsson]

Currently it looks in CWD of where you launched the app. For all current uses (gnome apps etc) these are the same. But, if they are not, i guess it makes sense for it to be in the same dir as the json.

[alexlarsson]

Fixed in master