The "Done" button was apparently meant for read-only events,
while the "Save" action was for everything else.
It didn't work correctly because of a mismatch between code and UI XML.
Fixes: https://gitlab.gnome.org/GNOME/gnome-calendar/-/issues/1142
Rewrite the text to properly market the app,
while avoiding referencing the target environment (GNOME).
Broadly emphasize the UX, existing key features, intended use,
and benefits of the application for the user in their day-to-day lives,
without over-selling it either.
We can augment this description in the future when more core features land.
Fixes issue #1109
These are still hardcoded instead of measuring the available space,
but it's better than nothing in the meantime.
Decent WMs size the window correctly if width/height exceed the screen.
Also, allow the Notes field to expand vertically, to fill the space.
Fixes https://gitlab.gnome.org/GNOME/gnome-calendar/-/issues/602
Jean-François Fortin Tam