SVGHMI: JS refactoring continued : "dispatch_value_to_widget" becomes widget class member "new_hmi_value" (was also broken by previous relativeness commit)

SVGHMI: widgets are not anymore binary relative or absolute, but have a "relativeness".

Because of allowing multiple variables per widget, we must distinguish if individual variables is relative to page, not the whole widget.

SVGHMI: More JS code refactoring : change_hmi_value and apply_hmi_value now methods of widget class.

SVGHMI: Better JS code semantic in ForEach widget class. Update lagging generated xslt.

SVGHMI: Add ForEach Widget is svghmi test

SVGHMI: add get_idx(index) to widget objects to factorize a bit code repeated accross widgets. To be continued.

SVGHMI: prefer apply_hmi_value() to change_hmi_value() when possible

SVGHMI: Add RelativePages to tests

SVGHMI: Update Widget Display templates to generate Class based declaration.

SVGHMI: JsonTable now picks items from HMI:List, and update texts, all according to Json data. Still miss scrolling.

SVGHMI: JsonTable now generate working data access code for data/* elements.

SVGHMI: Minimal support for HMI:List : clones pointing to elements of any HMI:List are never unlinked, widgets using HMI:List will rely on this.

SVGHMI: minimal JSON Table Widget communication infra + corresponding python code as py_ext code in svghmi test. To be continued.

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

Python Runtime : stil untested optimization of Python Safe Globals.

Now only one python_poll block per python extension is used to trigger
execution of OnChange calls.

Prevent global python_poll blocks to be created when accidentally adding content to C-File OnChange column.

Merge from default

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.

merged

SVGHMI: Fix bug introduced when merging default

SVGHMI: Add use of Python PLC Globals it test

Merge default changes in SVGHMI

Merge default changes in SVGHMI

SVGHMI: add "unsubscribable" property to widgets in order to generalize what already happens for jump buttons.
In most cases jump buttons do not really subscribe to pointed HMI variable, path is given as a relative page jump path. When widget.unsubscribable is set to true, no subscription is made on page switch, but still offset is updated.
This fixes bug happening on relative jump buttons without "disabled" element where offset did not change on relative page switch.

merge

Merge

SVGHMI: Added widget toggleButton.

SVGHMI: Changed widget button handler to element attribute.

Runtime: create .md5 file at the end of all transfered files being written to disk, so that it presence indicates completeness of transfer.