R1:629fa368cb9a

Calendar: fix creation of ICS Files

Summary:
It seems that, in an attempt to make ICS URI(s) editable, we broke the ability
to manually import ICS files. Whops.

The cause is, the URI needs to be put inside its dedicated import engine,
and not the general one.

Since the intention of T15137 was to be able to edit this field, we have done
that in the right way this time. So, you see the field, not just in creation mode.

Thanks to the kind aklapper for reporting.

Ref T15137
Closes T15619
Rollback…