In practice, the name and color widgets are currently meant to be used
when creating a local calendar, not when subscribing online, especially
as a single online calendar link can bundle multiple calendars.
This makes the scope of those widgets clearer,
and also makes the dialog more balanced.
Related: https://gitlab.gnome.org/GNOME/gnome-calendar/-/issues/566
Replace the manually positioned & styled group label by a property
This simplifies the XML code, makes the style match the rest of the UI,
and prevents libadwaita from sometimes moving such labels to the bottom.
Now that the "Open" button has been removed,
it is now a feature to "Connect" rather than "Import",
so update the section title to reflect that.
Also give a hint as to what protocols are supported.
A file imported as a "new calendar" would make it dependent on the file.
This feature was confusing everybody and is downright dangerous.
This does not prevent anyone from creating normal calendars,
and importing events from .ics files into them.
Fixes https://gitlab.gnome.org/GNOME/gnome-calendar/-/issues/390
Due to some languages using the "nplurals=1; plural=0" plural form,
and the string already in use in src/gui/calendar-management/gcal-new-calendar-page.c
with g_dngettext, add context to the other "Add Calendar" strings to fix the problem.
AFAIK, other locales (confirmed: be_BY, fa_IR, id_ID, kk_KZ, ko_KR, my_MM, zh_CN)
are also affected by this issue.
Move the add button from the headerbar into the dialog, make it
a pill button, and update the button label with the number of
calendars that will be added.
The interfacing that GcalCalendarManagementDialog had is somewhat
similar to AdwNavigationView, with pages and signaling basically
matching the same semantics.
We can save some code by switching to AdwNavigationView then, as
the heavy-lifting of page management is done there now.
The headerbar of the dialog is no more; instead, each page has its
own headerbar that automatically gets a back button.
Page activation and deactivation works essentially the same, but
uses AdwNavigationView signals to manage that.
The implementation of the credentials popover has relied on a hack,
and sadly this hack doesn't work anymore.
It's too late for a redesign, so for now, just put it into a dialog
and show it on top of the calendar management dialog.
The color chosen in the new calendar page is currently ignored
when creating a new calendar, as described in #681.
Added a callback similar to that used for the name text entry,
allowing new calendars to be created with the chosen color.
Closes https://gitlab.gnome.org/GNOME/gnome-calendar/-/issues/681
