SVGHMI: apply per class overloading of sub/unsub to Jump widget

SVGHMI: apply per class overloading of sub/unsub to ForEach widget

SVGHMI: Widget's specific sub/unsub traits are now wxpressed in widget's class.

SVGHMI: Parameters common to all widget constructors now passed as ordered parameters.

SVGHMI: One class per widget type, widget objects are instances of these classes, and members are passed through constructor. This allows to keep compatible with previous widget_defs template used in most widgets.

SVGHMI: Add an exslt function to collect used widget types, in order to only include necessary JS definitions in furure changes.

SVGHMI: Systematically output local name as /* comment */ when emiting content.

Merge

SVGHMI: Fix flawed logic to place nodes in the HMI tree, leading to wrecked tree in some cases.

Added button and circular bar widgets.

SVGHMI: added more meaningful namespaces to emit javascript code from.

SVGHMI: moved JS code of foreach and jump widget in corresponding widget_*.ysl2. To be continued.

SVGHMI: spread JS code from svghmi/scripts.ysl2 in other .ysl2 files, using dedicated preamble and epilogue namespaces

SVGHMI: Introduced "emit" to simplify producing per-topic code and content from anywhere in code. Applied to debug output, next to JS.

SVGHMI: Move reflective debug tags from "reflect" to "debug" namespace, preparing for per-purpose namespaces.

SVGHMI: Added scripts.ysl2

SVGHMI: moving code wher it belongs, and reformulate some declarations for better readability.

SVGHMI: HMI:DropDown: more documentation.

SVGHMI: Comments in HMI:DropDown source code

SVGHMI: HMI:DropDown menu aligns to selected when opening

SVGHMI: When clicking outside of opened HMI:DropDown box, close it.

SVGHMI: Fix HMI:DropDown flicker on close.

SVGHMI: HMI:DropDown now temporarily takes content from widget's arguments, until HMI:List is implemented.

SVGHMI: Connect HMI:DropDown to value in HMI Tree, in svghmi test as well.

SVGHMI: fix probable problem in HMI:Input, where value could be applied to wrong index if used in relative page.

SVGHMI: HMI:DropDown element is brought in front when opened, so that it isn't occulted by other widgets at the same level.

SVGHMI: HMI:DropDown now catches all clicks when open

SVGHMI: Add button element to HMI:DropDown, also fix problem with computed box margins.

SVGHMI: HMI:DropDown now scrolls forward and backward

SVGHMI: progress on HMI:DropDown - now selects some value on click, and close

SVGHMI: HMI:DropDown work in progress, intermediate commit. Now menu's rectangle grows up to viewport borders.

SVGHMI: intermediate commit while working on dropdown widget.

Here is the plan :
HMI:DropDown : svg:g of svg:rect + svg:text
rect is extended to match content size, and if content size exceed page size, user can scroll
HMI:List : either HMI:List:ListName as svg:text, one tspan per list entry
or HMI:List:ListName:Foreach:HMI_CLASS:SUB/PATH/TO/VALUE@/ROOT/PATH as empty svg:g

SVGHMI: HMI is not speculating on PLC variable update anymore when sending new variable value.

HMI variable cache in JS was changed in advance for more responsive behaviour when updating a HMI tree variable. This was leading to display value different from hmi tree variable in case the expected update did not happen because PLC program did revert it.

SVGHMI: finished shift and capslock support n keypad widget. Added a helper in widgets_common to collect subelements likle active/inactive/disabled...

SVGHMI: fixed keypad JS regarding shift/capslock and other details

Fix unmatched "Courier" font for monospace fonts on latest ubuntu 20.04. Selected "FreeMono" instead, present since at least 18.04

SVGHMI: Keypad working for HMI_STRING, still Shift/CapsLock not finished.

SVGHMI: fix keyboard not showing

SVGHMI: Added keypads to svghmi test's SVG file

merge

SVGHMI: Keypad: added code to re-attach keypad when starting edit.

SVGHMI: removed debug code

SVGHMI: More infrastructure for editing values with a keypad.

SVGHMI: Widget input buttons should be clickable through svg:use (onclick attribute instead of addEventListener)

SVGHMI: moved dead code to where it belongs

SVGHMI: empty widget_keypad.ysl2, WIP

SVGHMI: HMI:Switch now accepts boolean values 'true' and 'false'

SVGHMI: Jump widget, if it has a 'disabled' labeled element, reflects value of the pointed HMITree variable by showing this element when value is False, and behaving normaly otherwise.