This removes the manual painting of the background via cairo and adds the correct color to CSS instead,
which should hopefully improve performance as we do less cpu painting like this.
For good contrast in both dark and light mode, the link color is now a semi-light gray instead of complete black, which had bad contrast in dark mode and good constrast in light mode.
Later, we can seperate color palettes for light and dark mode, but only together with a dark mode toggle button or system-wide darkmode toggle.
Previously, these were defined directly in the code,
but defining them in the css helps seperating theming and behaviour
and makes the colors easier to tweak.
cargo.sh previously used bash features but only used `sh` in the shebang,
and also did not properly quote some variables to avoid splitting/globbing from happening.
Also, `-euo pilefail` is now set to avoid other errors that might come up.
This adds one new app icon and one new symbolic icon, and makes meson install these to the appropriate
directories, and adds an appropriate entry in the .desktop file.
While the position of a node not on the graph should never be requested, this seems to occur sometimes,
so instead of panicking, we only log an error now, or ignore that node if it wasn't
important.
to the left side of the screen. So by adding a constant offset,
we can avoid having possible links that are partly out of the view
just after starting the program
Links can now created by dragging in both directions, so now from an input port to an output port, too.
The drag-n-drop handlers now use dedicated types for each direction, so that no mismatched things can be dropped on each other.
Control points are now offset by half the x distance of the start and end points instead of a constant,
which makes the curve scale better with varying distance.
While the properties for a links node ids are not always set, they always are in the link info.
Also, the work done in this commit will easily allow to get the format of links and ports later,
so that we can get the format of them much more reliably,
and we can also get notified of changes to an existing global via the info callback.
This is more reliable than assuming the link carries the id of its nodes, as there have been cases where a link was created without those
properties set.
Instead, we can just pull them from the state via the port ids of the link.
Glib MainContext is now aquired manually because a change in gtk-rs would lead to
a panic when attaching the receiver otherwise, because gtk::init() doesn't
"leak" the default main context anymore.
