Auto-create layers for Brushes, Gradients

Add automatic layer creation for Brushes, Linear Gradients, and Radial Gradients. Currently, a layer is created only if there were no layers before. Add automatic layer creation for the main tools so that they don't accidentally overwrite the current layer. You can do the same thing as it works in the Style-brush tool, with auto-switching of the layer, if you apply an already created type of brush/gradient.