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.

Modbus plugin: reformat code, and add comment.

Modbus plugin: fix runtime periodic timer (don't use POSIX timer)

Modbus and Bacnet websettings : Rename variables and functions to avoid name collisions.

Websettings for modbus and bacnet are now passed to runtime as python files loaded (execfile) at init of PLCObject with the same globals.
Because if this, same names used in previously different modules now colide.

Modbus: fix strange side effect of re-use of condition variables or mutex with Xenomai : without bzero of the associated types, mutex keeps locked.

Modbus: fix client timer invalid arguments.

Modbus add a timer thread, and switch timer to SIGEV_THREAD_ID to follow xenomai posix skin restrictions.