It will be easier for some commands to generate an action text on the
fly instead of having to think of it up front, so a virtual that you
can override seems more convenient here.
When pushing a new command on an undo stack, we will now attempt to
merge it into the stack's current command.
Merging is implemented by overriding the "merge_with(Command const&)"
virtual on GUI::Command. :^)
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 *
