Now happens when JS canvas want toggle log states

Later such specifier can be used to access object parts like axis.
For the moment is not relevant

Use no_root_json and no_h_json URL parameteres.
Automatically applied for webcanvas

Let retrieve latest canvas version even without explicit
Canvas::Modified() call

Support jpeg, png and svg formats.
All formats transformed now in base64 coding

this affects the order in which the libraries are loaded and ultimately
the order in which the streamer infos are present on the files.
This affects the roottest-root-io-filemerger-make test, very sensitive
to the file size on disk which in turn is sensitive to the size (and compression factor)
of the TStreamerInfo record.

Let use openui5 with the CEF

It sends regularly from the JS client to avoid closure of websocket
connection. Also let verify that connection is still available

This refactors the CMake build files to no longer manually call
the CMake functions for generating and linking the dicionairies.
One reason is to reduce boilerplate, the other is that it is now
no longer possible to have naming mismatches between the dictionary
generation arguments and linking function arguments which was causing
the race conditions we had in our build system.

This also now follows more strictly the separation between dependencies
like Math, Tree and Core and pure linking flags to external libraries.

When canvas window should be opened with external browser, real HTTP
server should be started. CanvasPainter will try to open several ports
in the range 8800..9800

Closes all connections to clients. As a rection, all opened window
should be closed. Currently worsk with CEF, Qt5 and local/remote
browsers

While it happens very fast, JS close handlers are not executed properly.
Therefore special JSROOT handler called directly when qt5webview widget
is closed.

When close message send by client, server clear all callbacks and
does not reply on the message. Still X is crashing if close called from
window.onunload handler

Invoked when current canvas version delivered to all clients.

Callback function called when file is created (or command fails)

When synchronous mode specified (defualt), 
method blocked until file is produced. 
With asynchronous mode method returned and file will be produced in
background. 

One can call Canvas::SaveAs() several times, all specified files will be
created one by one asynchronously

It let configure more complex program arguments for starting browser for
the canvas, provide brief docu

By defauly, ROOT will try to crate local window with CEF or Qt5.
If not available, default browser will be started.
If place is specified, it should be program name like:
   canvas->Show("/usr/bin/opera");
   canvas->Show("firefox");

One could show canvas in several different places.

By default, TCanvas::Update() will block until latest canvas 
version delivered to all clients and displayed. Implement with
straight polling loop.

Each call to TCanvas::Modified() increments modify counter. 
This counter used in then next TCanvas::Update() call to identify
current version of canvas. TCanvas::IsModified() will return true 
until drawing is completed and painter confirms that last version of
canvas delivered to all clients and displayed. 

Same as with CEF, X still initialized