This commit adds a `ColorSelectOverlay` class, and uses it to
allow the user to pick a color from the screen. The API for
`ColorSelectOverlay` is inspired from the `SelectableOverlay`
in `Utilities/shot.cpp`. In particular, it opens up it's own
window, so that we can have control over the cursor over the
whole screen.
There's one thing notably different: In addition to returning the
final selected color from the `exec()` function, it also provides
an `on_color_changed()` hook, which can be used to (optionally)
get live updated as the mouse is moving around.
This is a bit odd, but allows us to use the preview widget of the
color picker to see the current color under the mouse (which will
be selected upon clicking). When trying to select the color from
text / other small elements, this is very useful.
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 *
