The `@theme_selected_*` colors are now aliases
to the libadwaita accent colors variables. This commit
replaces all uses with the corresponding color,
except for the text colors.
`@theme_selected_bg_color` is not the appropriate color
to use for colored text. Instead, you should use
`@accent_color` which has been tested for proper contrast.
GcalEventPopover gives a preview of the event, and handy access
to the event description and information. It also allows easily
joining meetings if any one if available.
The list of supported meeting URLs is small now, but I hope
more people will contribute as we go.
It is also possible to edit the event through an edit button.
