Merge + fix side effects of making warning instead of errors in case of missing HMI variable

Updated svg and xml for testing program

Button, ToggleButton and slider updated. Error to warning when building

Button fixed so it doesn't release until it gets feedback from plc

Toggle button changed so it makes changes instantly. There was too big delay if we waited for feedback.

Slider added new features need some changes for final version.

Modbus: fixed typo in ctype typing.

MODBUS: Fix saving of websettings.

Runtime/PLCObject : move call to PreStartPLC right after call to the "start" method of all python extensions, and then just before the start of the python loop executing python_* blocks.

SVGHMI: Better error message when inkscape is not installed.

SVGHMI: nicer error message

Merge

Attempt to workaround problem reported about empty plc.xml after unrelated crash. Now, if etree model is corrupted in a way tostring() would generate an empty string, exception prevents saving.

SVGHMI: JsonTable can now have clickable elements, that trigger a request with extra argument whose content is taken from Json data.

Merged

SVGHMI: cosmetic fix in test

All widgets reworked to use widget class and animate function if needed

SVGHMI: Moved JsonTable/Alarm related test in a separate page.

SVGHMI: JsonTable now ignores elements and groups starting with #

SVGHMI: Fix keypad : non-number input was always considered invalid because of missing type checking.

SVGHMI: JsonTable now updates range and position variables so that slider widget can update.

SVGHMI: Fix multiple variable support in widget

SVGHMI: Add TODOs in Button widgets.

SVGHMI: Alarm test not using Button widget anymore, too many problems. Use Input widget instead to increment value on each click and execute python code on change.

SVGHMI: little fix in HMI:Button

SVGHMI: JsonTable now use intermediate variables again to address JSON data without duplicating code or referencing. Using intermediate variables also alows to check for availability of data and stop evaluating early if data is missing. Finally added complete roundtrip example to illustrate use of JSonTable to display "alarms" collected in python from changes on PLC boolean variables.

SVGHMI: removed debug code forgotten here and there.

SVGHMI: JsonTable now makes meaningfull JSON request : all arguments and variables are passed in.

SVGHMI: Keypad is now keeping Javascript type constency. In other words, if a number was given as initial value, input value will have to convert to number in order to be valid. In case invalid value is entered, initial value is restored.

SVGHMI: Behave when project path include spaces, and make more understandable error in case of problem extracting geometry with inkscape.

SVGHMI: Refactor the way JsonTable generate javascript code to access json data. Now support multiple assignments, used in the case of text to change both content and style on the same element.

SVGHMI: Fix again clone unlinking, and this time add an "original" attribute to track the id of the original object before unlinking.

SVGHMI: Fix svg test file while testing latest JsonTableChanges