new module development: Packing Slips

[Guido1982]

I've started a branch in my repo to setup a proof of concept for creating a more modern, OOP way of handling inventory modules. Installing it will bring you a mess, but things like sorting the lines by dragging (in edit view) work, just to get a feel for it. Apart from that I moved a lot of code into a class and removed a lot of javascript from the template file. No replacement for this yet, but the plan is to create an OOP style JS object for inventory lines as well. The goal is to create code that could work with the current inventory handling, but could easily be adapted to work with Inventory Details module.