* Do not attempt to unref or destroy a child of a container

*In GTK 3 at least, GtkContainers automatically destroy child widgets when destroyed

As done for copy/delete jobs, restart the operation timer also for move
jobs. Thus preparations (e.g. `scan_sources`) later won't affect the
later transfer rate calculation.

caja-file-operations: stop timer when waiting

When a copy/move operation is created while another operation is already
active, the new operation is queued. As the (already running) operation
timer of the new operation is not stopped during the waiting period,
that period is (erroneously) included in the transfer rate calculation
and leads to initially low/slowly increasing transfer rates be shown.

Hence stop the operation timer when the (queued) operation is waiting.

Fixes #1420 and #1623.

* caja-file-operations: fix estimate for queued copy

Fixes the condition for showing an estimate of the remaining duration in
case a copy operation is queued, correctly considering the current
transfer rate.

* caja-file-operations: fix division by 0 for delete

Aligning to the copy operation case, this fixes the condition for
showing an estimate of the remaining duration for delete operations,
preventing a possible division by 0 due to a zero transfer rate.

*Do not use G_OBJECT_CLASS (class)->constructed
*We don't seem to need it anymore and it breaks dragging windows with the titlebar or resizing with the mouse in wayland

It is totally unused. In 2010, nautilus removed a perl script used to
generate enums:
https://gitlab.gnome.org/GNOME/nautilus/-/commit/75a03a440ebff23ccbf8674ca4a0e9f6475ebbb8

Before then, perl was needed to build. After this commit, nautilus still
had messy code to check for perl availability but did nothing with it.
Across multiple forks and reinitialized git repositories that dropped
all commit history, it turns out that caja still has that messy code
too.

*In the wayland session, we now have mate-settings-daemon with GDK_BACKEND=x11
*We need it anyway to control theming in xwayland apps,so we can now use mate-appearance-properties to set the desktop background when it is running