SVGHMI: i18n: ensure langs always appea in same order, and add two variables that are updated automatically when selecting a new language : lang_name and lang_code. Also fixed i18n startup, prevent wrong lang numer to crash loading.

SVGHMI: more straightforward implementation of dragging position computation in Scrollbar + some little fix about boundaries.

SVGHMI: allow i18n of formated strings of HMI:Messages. This was by construction impossible since formating was given as an argument. Now added optional "format" labelled element in HMI:Display, so that it can be translated, when labelled "_format".

SVGHMI: update generated XSLT

SVGHMI: i18n: prevent creating messages.pot if no translation

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