We call "change_document()" in this case, which only switches the
document without creating a new window and consequently did not do
any of the required set-up

This ensures window size/position and other preferences stored in
<namedview> are properly applied.

- re-fix Cmd-Q confirmation dialog (#383) without the numbers typing regression (#385)
- re-fix Alt modifiers (inbox#765)
- fix Cmd-A select all text (inbox#765)

Bug occurs with programmatic resize at startup
Fixes https://gitlab.com/inkscape/inkscape/issues/125

Any change from previous behavior is a bug.

The call to
  Gdk::Display::get_monitor_at_window()
in
  Inkscape::UI::get_monitor_geometry_at_window()
requires the underlying GdkWindow to be fully initialized.

This is achieved by calling "realize()" before attempting to read
that information.

Previously we used to show the window first (which implies realizing
it) which worked around the issue. However it required us to hide
and show it once again later if we wanted to move it in order for
the window manager's routines to sanitize the position to kick in.

It was accidentally dropped in
  8b1840f9507f10911f63fc00b9885354ead99d53

Also show window *after* setting position/size. This gives the
window manager the chance to move an off-screen window back into
the visible desktop bounds (e.g. after a monitor was disconnected).