Histogram stat box update
Do not use variables before define them
Remove unused variables

Use RDrawableRequest to configure individual zooming ranges and
use them in RStatBox for histogram statistic calculations

Exact info about lines delivered with object - can be adjusted for each
statbox subclass in the future

Provide generic Execute() for RDrawable class, 
allows to execute all methods markes as **MENU**
Later one can provides attributes changes via menu

Use RDrawableRequest for changing drawable attributes 
and for requesting menu items

Preliminary client code for RHistStatBox

When palette does not explicitly provided in drawables,
create default RPalette and associated it with RFrame

Now it is plain class - no any complex attributes members

Let draw palette, perform zooming

Complete class renaming

Doing in two steps to keep git rename history clear

Each margin can be coded as string like "10px + 0.1"
Simple parsing is provided.

Potentially one can use RBoxAttr, but let not do it too complicated

Allows properly inject many messages at once

Used in eve for element selection

Add support of TGeoTessellated 
Reverse axes in TH2 col plots
Better support of TLatex topline/underline/crossline

Use JSROOT ProduceImage functionality.
Only if image name ends with "*shot.png", chrome --screenshot
functionality will be used

Using --dump-dom functionality of the chrome browser to store complete
HTML file and then extract only part of it

Try to use --print-to-pdf=filename.pdf argument of chrome browser
 

Image generated using same snapshot as for online case
Original RCanvas is not required

Instead of running complex websocket communication in headless mode,
run chrome browser using file system. 
In that case no any http server is required!

Draft for png, jpg, gif images

Fix problem with connection closure for qt5 web engine
Improve highlights handling for TGraph

One should remove cross-references in destructor, otherwise RWebWindow
object will never get destroyed

Corresponent part of RWebWindow functionality

Support geometry light configuration
Support openui5theme config
Error handling when try object draw in non-existing HTML elements