removed the deduplicate select-first-option code now in favor of the one in firstUpdate
also automatic convert empty_label for et2-select multiple into a placeholder
- fix missing app select
- add clear button
- use request() instead of json() to query server
- add optional class property to SelectOption
- move cleaning select options to its own function so we can use it anywhere
- Use separate render to keep local / remote options separate. Local options stay in select_options.
- get_select_options seems to be nowhere in use, so I did not implement it
- Et2Select* widgets with static options assign them in their constructor (like the r/o ones)
- removed a jQuery.proxy call, which we dont want in new code
Any child that has selectbox type functionality (extends Et2WidgetWithSelectMixin) needs to implement:
- _optionTargetNode() : HTMLElement
- _optionTemplate(option : SelectOption) : TemplateResult
