screen-time: Add initial Screen Time panel and implement break reminders
This implements the break reminders section of the design from https://gitlab.gnome.org/Teams/Design/settings-mockups/-/blob/master/screen-time/screen-time.png.
It’s to be used in conjunction with the new settings schemas and gnome-shell changes:
- gsettings-desktop-schemas!78
- gnome-shell!3251 and also has associated documentation:
- gnome-user-docs!172
Signed-off-by: Philip Withnall pwithnall@gnome.org
Helps: Teams/Design/initiatives#130