Loader now adds a layer instead of opening a file in Photoshop

This branch implements the Add To Layer action for the loader. It supports both images and PSDs.
The 3 main tasks were:
- Renaming the Open File action to Add To Layer.
- Adding a check to make sure there is a current document.
- Using the Place action to create the layer.
Reading it here again, it seems so preposterous that I had to triple-check. I was right.

I just did some extra research and found this: http://www.pcpix.com/photoshop/enum.htm
It's a rosetta stone that translates 4 letter charIDs into stringIDs which are more cleaner to read. Still doesn't have any documentation on what these parameters do, but at least it's cleaner. I'll update the code to reflect that.