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.
"Add to layer" sounds like we are adding it to an existing layer! But then the description says "Adds a layer..." - This seems confusing to me! Is it creating a new layer in the photoshop image? In that case, should it say "create new layer"?