Implement "set-property" handling in dbp-provider and use it in dbp-language-select (dbp/apps/library#77)

Add a scope so we don't have to care about naming conflicts
and set the verison to 0.1.0 since we don't have a stable API yet.

We only want to export it in the package entry point and not
the generated bundle.

The demo now registers our web components lazily with a unique name
so that two different apps using the same underlying web compontens
don't clash.

This also disables auto registering and leaves that to the user.

Just use the inherited one set by the user.

to be in line with the logo

This duplicates the language switcher on the tugraz.at site.

Compared to the previous implementation we now show the next language
and use the translations for the next language, so that users only knowing
english can understand it.

In case of more languages we just cycle through them, which isn't ideal but
good enough for now.

So we get errors with older browsers.

So we can use it directly in lit-element templates and don't have to
add an event handler to window etc.

update() is called before the actual update so we need to change i18next there.

We now listen to our own signal so multiple language selects on the same page work
and are kept in sync.

Also use the same reference for removing the event handler, bind creates a new one.