Reusable windows instead of popovers

[sim6]

This changes improve noticeably the performance when list a lot of tasks.

[mrvladus]

Looks good, but I don't think we need details window. Popup is enough. And you can remove RAISED style for ToolbarView. And for the priority window we need to add navigation-sidebar class for ListBox. I wanted to redisign it later, but it will be good for now.

[sim6]

Thanks. I removed RAISED style and added navigation-sidebar class. About window Details, with the current code there are a menu with color widgets for each task, so a lot of widgets in a list with a lot of tasks and raises for each new task, but with window Details the number of widgets are fixed and reused for each task.

[mrvladus]

Is there any way we can reuse popups?

[sim6]

Sure, but I prefer Adw.Dialog because I like the application more homogeneous and also it is more usable on small touch screens like the one Librem5 comes with.