Add a little test to see OnChange's .count .first .last in action

Fixed "Onchange" object added in previous commit

Python Safe Globals now have more reliable triggering of OnChange call. Added "Onchange" object to accessible runtime variables that let user python code see count of changes and first and last values.

SVGHMI: cosmetic fixes in button widget

SVGHMI: Rewrote button widget.

SVGHMI: update generated XSLT

SVGHMI: stuff test so that it moves all the time, to have better chance to spot memory leaks...

SVGHMI: prevent unwnted context menu and pinch zoom

SVGHMI: more attempts to prevent losing memory in JS closure

SVGHMI: WIP trying to reduce memory usage : use .onclick onstead of SetAttribute, avoid useless closure and object creation when possible, etc.

SVGHMI: update generated xslt file

SVGHMI: use const when applicable

SVGHMI: prevents text and svg elements selection on the whole page when dragging.

SVGHMI: Update default test to check that Input widget is indeed updated when variable changes.

SVGHMI: Fix: on screen keyboard wasn't showing up when editing local variables through Input widget.

Project tree: avoid flickering and glitches in notebook when selecting some still not opened ConfigTreeNode