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.

Runtime: Fix typo in PLCObject leading to exception when reporting failure.

Py_ext: use non-derived type when generating C code for handling Python PLC globals.

tests/python : add some STRING PLC Python globals with OnChange.

Runtime: STRING type for Python PLC Globals was making problem with strings, since generated code wasn't doing comparison properly.

Merge

Modbus: more comments to remember some necessary changes.

Modbus/BACnet : add some comments so that we don't forget some pending optimization.

Modbus: Delete stored configuration when identical to default configuration.

BACnet: prevent saving configuration that is same as default, delete it if so.

BACnet and Modbus : fix configuration storage directory

Runtime extrension web settings: distinguish display string and token when calling NS.newExtensionSetting, thus allowing meaningful name to be displayed instead of an id.

Debug : when BEREMIZ_DEBUG file exist, display all commands issued in console.

BACnet and Modbus : Simpler configuration management. NevowServer.py now allows each extension to create and delete multiple configuration forms in the setting page, deprecating delSettings and addAfter.

BACnet and Modbus: Remove additional loading and unloading, use the one already in place for extensions.