[Pas2js] htmlwidgets add combobox support

[Mgr. Janusz Chmiel]

I Am kindly asking you. If you would have some time on future. Could you add
Combobox support to htmlwidget unit? It is very useful GUI element type.
Do not be afraid. YOu have added The most important GUi widgets. But
combobox could be add too. I only do not know, if is it possible to
implement such widget object by using Pas2js Pascal language. If there is
not an complex relationship between Javascript and Pascal which would
prevent you from adding this widget type to htmlwidgets unit.

I have started to study yours unit deeply. I have started to inject and add
all procedures names to A separate file. I have added widgets classes to A
separate file. And my approach have been very useful for Me, because I would
be able to add clear text to The WEB page, button. Today, I will try to
implement click procedure.