Fix unmatched "Courier" font for monospace fonts on latest ubuntu 20.04. Selected "FreeMono" instead, present since at least 18.04

Python Runtime: order of execution of extension's init() and cleanup() now reflects order of appearance of extensions in configuration tree.

Runtime: change PLCObject 'BlobAsFile' method to allow customization by overriding

WebInterface: better wording for wiping PLC content: "Repair"

runtime: added restart/reset button in web settings. Accidentaly fixed web settings logging feature.

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.

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

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.

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

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

PY_EXT: OnChange is now a coma separated list of callables. Updated tests/python accordingly.

Modbus: fixed typo in ctype typing.

MODBUS: Fix saving of websettings.

Runtime/PLCObject : move call to PreStartPLC right after call to the "start" method of all python extensions, and then just before the start of the python loop executing python_* blocks.