This in turn emits an 'activate' signal that any applet can connect to
and perform whatever action it means to activate in that applet.

This allows users to control certain applet functionalities through
DBus, like registering new keybindings, or integrating them with other
software.

We need to check the existence of dconf-editor's GSettings schema before
using it, because the program will abort if dconf-editor is not installed
on the system when it tries to access it.

Mostly found by cppcheck.

origin commit was:
https://github.com/mate-desktop/mate-panel/commit/96c7ebc

This reverts commit 96c7ebc6dc9e8b8327db04a9570054ee78743353.

*Fix the window list menu replacing the panel context menu between the end of the window list and the next applet

Mostly found by cppcheck.

- Build the list in reverse order, then reverse the result.  This is
  useful because GS?List are list nodes, not containers of nodes, and
  thus don't contain a pointer to the list's end, meaning to append one
  has to walk the entire list to find the end each time.  To avoid this
  we use the common idiom of prepending to the list (which is cheap, as
  it's adding a node before the given one), and then reversing the
  resulting list to get back the original order.
- Avoid unnecessary memory copy by stealing the GStrv's members.  We
  get the array as a copy, so we can simply steal the members and free
  the container array only, saving a copy for each member.

* There is only one screen in GTK 3.22 or later
* Finding the screen from that used by GtkPanelPlug is out of process only
* Any in-process applet calling mate_panel_applet_request_focus needs this to avoid a segfault
* One known user: dictionary applet