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.