Modernize status icons

Hi,

I noticed that Evolution Alarm Notify has a nice new modern icon in the Adwaita theme, but that the status icons, for example for new notifications, didn't. So, I have made this pull request to fix that. These icons are from the symbolic svg version of the same icon from the Adwaita icon theme, that I have exported as a png for every size.

Here's an example of what these icons look like:

This is something that's been bugging me for a while, as you can't escape the original icon if you use GNOME Calendar, even as a Flatpak, so I'm hoping this will get get merged. Thanks for developing GNOME!