FMod - Allow keeping the selected tile crosshairs around

One Abiathar user said that it would be nice to keep the selected tile crosshairs showing even when the Palette Copier is the active tileset tool. I originally hid the crosshairs when using that tool because they could get in the way of seeing the block you want to copy. When using the Palette Copier as the primary tileset tool (for Keen Next emulation), though, that leads to virtually never seeing the crosshairs, which is disorienting. So today I implemented a simple new configuration option that causes the selected tile crosshairs plane to remain visible even if the current tool wants it hidden. I also put a checkbox for it on the Tools tab of the Settings dialog.