Try to be more consistent that related options should have a group box
around them.

This is what pretty much everyone else calls these kind of settings, so
let's change so users feel familiar.

Try to focus on the commonly used settings here in order to keep things
understandable. The uncommon settings will need to be specified as
command line arguments instead.

Clarify what this list is used for, and organize it so it is easier to
match to the options dialog.

We raised the requirement in cb3c78f but forgot to update the
documentation.

VENDOR_STRING is gone as is DEFAULT_LOG_VERBOSITY
site.h has been removed and is not needed.

Be consistent in "full screen" and "full-screen" use

Previously, there were a number of inconsistencies in the use of
"full-screen" and "full screen" in logs, documentation, and user
interfaces. The consensus seems to be that "full screen" is correct when
used as a noun while "full-screen" is correct when used as an
adjective. These inconsistencies have now been adjusted to follow
consensus.

Deduplicate vncviewer error messages

vncviewer previously had a the same localized error message duplicated
on a bunch of places. Pull these duplicates out into a single function.

It's difficult to support both old and new versions, so raise the
requirement to the oldest that is commonly used, which is CMake 3.10.2
on Ubuntu 18.04.

They don't really contribute to anything as the command line is fixed,
and it makes CMake 3.20+ upset since it cannot find that file and
instead thinks we meant maketarball.in (CMP0115).

This version of Ubuntu is no longer fully supported so let's stop caring
about builds there.

Can be helpful to see what encodings were actually used during a
connection, and how they performed.

macOS' built in VNC server unfortunately sends the entire monitor in a
single rect, so we need to be prepared to buffer a lot of data in case
the monitor has a large resolution.

Gives a bit more context where this error happened.

Single CPU machines are extremely rare now, so let's avoid the hassle of
multiple code paths.

If you close the reconnect dialog then we should assume that you want to
close things, not that you want to reconnect. Unfortunately FLTK returns
the first choice when closing the dialog, so that needs to be the
"Cancel" alternative.

The certificates might still be fine using the system trust store, or
the user can make an exception. So let's just log and continue on.

This got very common after 960c7d2 where we now always have a default
value for these settings.

Workaround FLTK bug that causes OptionsDialog to appear behind DesktopWindow

FLTK's fullscreen_x() function will always put the window on a high
level (NSStatusWindowLevel = 25), even if the window doesn't have focus.
This causes the OptionsDialog to end up behind the DesktopWindow when
the fullscreen function is called. Until we can rest assured that most
people building TigerVNC will use a fixed version of FLTK, we will need
this workaround.

Remove modal property from ServerDialog

Modal windows are meant to be child windows such as menus or popups that
are intended to always appear in front of its parent.

Modal FLTK windows without a parent seem to behave strangely on macOS.
Such windows can appear in front of their modal children windows.
When opening OptionsDialog from ServerDialog, it was easy to get to a
broken state by then switching focus back to the ServerDialog. This
would cause the ServerDialog to appear in front, but not be useable as
the options window would still have control of mouse and keyboard.

Additionally, modal windows without parents appear in front of other
normal applications on macOS. This means that the ServerDialog couldn't
be put behind Safari for example.

The fact that ServerDialog was a "modal" window was a bit strange,
seeing as it doesn't have any parent windows. Removing the modal
property from this window causes all the strange-ness to go away.

Only grab keyboard when we have focus

There was an issue with the new grabs that were introduced in commit
2289342de7. On macOS when running
vncviewer in fullscreen on one monitor, we saw that we sometimes got
resize and fullscreen events when switching the focus away from
vncviewer. With the changes in the commit mentioned above this meant
that we immediately grabbed the keyboard again, thus never releasing it.

Fixes #1332.

If a monitor is part of a set of mirrored monitors, then give the name
of all used monitors as we don't know which one the user will most
strongly associate with what they see.

The device name is very internal and likely of little use to a user.
Instead give the more user friendly string we can get out of the system.