SVGHMI: Add inhibition to widget's apply_hmi_value() so that it does not change variable more frquently than given widget's frequency. This prevents flooding network with many update if browser is producing events at high rate, as for exemple when dragging ScrollBar's cursor.

SVGHMI: fix scrollbar not behaving when rotated.

SVGHMI: remove forgotten debug code

SVGHMI: Add a robust ScrollBar widget. HMI:ScrollBar@positionrange@size

SVGHMI: propagate default local variables (HMI_LOCAL, PAGE_LOCAL) to widgets at startup

SVGHMI: Update generated XSLT

SVGHMI: HMI:DropDown:#langs@lang now automatically shows human readable list of languages. tests/svghmi_i18n updated accordingly.

SVGHMI: Add a simple i18n test

SVGHMI: Prevent Dropdown widget to mak exception whe value out of range

SVGHMI: removed dead code

SVGHMI: Add "lang" permament persistent HMI_LOCAL variable to reflect selected language, apply stored language choice at startup and make it always subscribed to a pseudo widget (as for hearbeat) that apply language choice when it changes.

SVGHMI: Added HMI:VarInitPersistent to initialize persistent HMI_LOCAL and PAGE_LOCAL variables, stored as cookies in browser.

SVGHMI: Enforce formating HMI_LOCAL and PAGE_LOCAL variables until the end of variable name

SVGHMI: generate JS translation literals so that it is possible to also translate uses of texts, and added JS code that apply translations to tspans

SVGHMI: widget activable elements : moved code to wher it belongs, rewrote cleaner