SVGHMI: factorize dispatch calling logic.

SVGHMI: HMI:VarInit:"a string"@a_value : empty widget (i.e. empty svg:group) that initialize content of local variables to value given as first argument.

Merge

SVGHMI: Add more local HMI variable tests in tests/svghmi.

SVGHMI: finished initial implementation of PAGE_LOCAL and HMI_LOCAL variables.

SVGHMI: add a SetPoint to Slider Widget, visible only when operating the slider.

SVGHMI: Update Slider widget so that it doesn't display future value but actual value only.

SVGHMI: provide request_animate() to Widget authors so that they can register redraw code when events lead to redraw. Widget member animate() is called when it is time to update DOM.

Merge

SVGHMI: Intermediate state while implementing local HMI variables. Now write to cache only (no send), still need to implement dispatch on change.

Beremiz test project with newly created widgets.

Rebuilded gen_index_html.xslt after all new widgets were commited

Create new multistate widget which extand class widget

Create new CircularSlider widget which extand class widget

Create new slider widget which extand class widget

Reworked togglebutton widget to extand class widget