* Allow to display tutorial images with JavaScript

* use find instead of find_first_of

* Output first <div>  then <script>

* Make sure each canvas size is the right one in case of several canvases.

This reverts commit a7d45455.

The Johnson PDF is a transformed Gaussian distribution. An implementation
with analytical integrals and generator functions is added.

Also:
- Test for equivalence with an LHCb reference implementation
- Test numerical vs analytical integration to percent level
- Test numerical mean value vs literature
- Add release notes and images for doxygen

the goal was to avoid tutorial names appearing as namespaces.
The change removes from the doc also the tutorials, which is not
acceptable.

* Fix doxygen generation with Python 3

* Adjust tutorials for doxygen documentation generation.
When run inside the makeimage.py wrapper during doxygen generation the
variable scope is different than when the tutorials are run stand-alone.
The change in tutorials/math/tStudent.py is Python 3 specific and is due to
that list comprehensions in Python 3 are run in an implicit function scope.

Done using the command "doxygen -u".

Having it set to YES makes all the python tutorials being referenced as namespaces.
This issue was reported in: https://sft.its.cern.ch/jira/browse/ROOT-9887

 * Document constructor of RooBukinPdf.
 * RooArgList
 * Improve doxygen for RooDataSet.
 * Measurement, RooBernstein, RooCustomizer.
 * Add VisualizeError to RooAbsPdf docs.
 * Update index.md files to also show roofit tutorials.
 * Fix typo in RooPolyVar docs.
 * Add image and description for RooArgusBG, minor improvements for RooAbsPdf and AsymptoticCalculator.

* Improve documentation of RooAddition.

* Improve formatting of docs for RooMCStudy and RooAbsRealLValue.

* Improve documentation for RooMCStudy and RooAddPdf.

* Improve docs for several Roo classes: RooAbsReal, RooAbsPdf, RooAbsRealLValue, RooExtendPdf.

* Minor improvement of docs in RooAbsPdf, RooExtendPdf, RooRealIntegral