Calendar edit modal should use `NcDialog` instead of `NcModal`

[st3iny]

Steps to reproduce

1. Edit a calendar.
2. Observe the modal.

Expected behavior

Great design

Actual behaviour

Headers are a bit too big. This can apparently be fixed by migrating to NcDialog.

Calendar app version

main

[st3iny]

This can't be fixed by moving to NcDialog unfortunately. This will make the main header be center aligned and the sharing header left aligned which doesn't look nice.

I'll adjust the header and reduce the height a bit.