This change fixes the initial tool selection when pixelpaint is started
with a path. Previously an already existing editor was expected when
the default tool was initially propagated - which was not the case if
pixelpaint was launched to directly load an existing image.
Since there's only one global toolbox, it makes sense to store the
active tool in here, since we don't really have control over the
deletion of an editor.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
