[Feature Request] Setting to automatically trim/expand layer size after image manipulation

[JordanMagnuson]

Part of Improvements to bounding boxes and rasterized layers

Option in program settings (checkbox in Tools -> Settings) to "automatically trim/expand layer size after image manipulation."

This would do two things:

1. Allow drawing outside of current layer boundaries by tools such as clone/blur/bulge-pinch. The full image canvas could be used, and then the layer would be expanded as necessary.

2. Each layer would be trimmed to the current pixel boundaries after any relavent image manipulation (e.g. select-and-delete or erase tool), maintaining the layer bounding box at the edge of the actual image size. (So for example if you select and delete half of a large layer, the bounding box for that layer will be updated to contain only the half of the image that is left on the canvas.) Would also trim layers automatically after Layer -> Convert to Raster operation.

See #287 (comment)

When this program setting is selected, then layer bounding box should only be shown when "select object tool" (move tool) is selected. Otherwise layer bounding box should be hidden. See conversation in Improvements to bounding boxes and rasterized layers.

[JordanMagnuson]

Better/simpler solution, I think, is simple program setting to "automatically trim rasterized layers when move/transform tool is selected." The layer expansion aspect can be handled by #300

(Keep in mind scenario where move tool is selected and user changes layers. -> new selected layer should be trimmed.)