Blender Git Loki

GP Edit: "Change Layer" operator - Integrated into the D+W Pie Menu

Create a "Change Stroke" operator for GP Layers which can be used to change
between layers without needing to have the layers list open. This can be
accessed via the D+W pie menu by clicking on the dropdown beside the active
layer's name. Also, added the ability to delete the active layer from the menu too.