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

merge

py_ext: better handling of coma separated OnChange attribute for python safe global variables.

Project tree: Clicking on ConfigTreeNode should have same behaviour as for POUS and other IEC types : simple click to select and double click to open.

Allow customization of generated py_ext OnChange calls, by adding a static method to PythonFileCTNMixin that can the be later hot patched.

Arbitrary variables added to JsonTable subscription are now passed as 'extra' field in json query. As an example added JsonTable filtering in tests/svghmi

SVGHMI: Fix HMI_REAL support, and add a HMI_REAL use case in tests/svghmi.

merge

SVGHMI: JsonTable now outputs "visible" value as well.