SVGHMI: added "page_node" variable that reflects the HMI tree path of current relative page

SVGHMI: Add list of HMI tree path in a JS array, so that we can use it for multiple purpose :
- display name of edited variable in keypads (currently wrong in relative pages)
- have some variable that hold basename of current relative page HMI_NODE's path
- propose some list of names in DropDown when selecting a relative page to jump to, without having to instancite many jump widgets.

SVGHMI: Fixed wierd CDATA mess in output xhtml, because of backticks copy pasted in some yml ||text block||