We now require at least 1.16, so remove all code that handled older
versions than that.

No longer tolerate loading the VNC extension but not being able to
initialize it. This avoids a lot of error prone checking to see
if the extension has started fully or not.

Allows to specify which configuration parameters can be modified on runtime.

Also handle clipboard transactions from the server to the client
directly in the server without the help of vncconfig.

Handle the clipboard directly in the server, avoiding the
dependency on vncconfig. This commit adds support for clipboard
from the client to the server. Handling of the other direction
will follow.

The REQUEST macro is used to access variables in the request data,
and if we don't then the compiler complains that the macro sets up
variables that we never use.

The internal Xorg headers are very incompatible with C++ and we've had
to resort to all kinds of hacks in order to include them in our C++
code. This approach isn't really viable long term so restructure things
so that we have a glue layer written in C that bridges the Xorg core
with the RFB classes.