refs #179

refs #179

Using the ID type makes type errors more likely because we accept a
wider range of types as arguments for API operations than we actually
support on a logic level, i.e. when using maps because

	Map<ID, T>.get('1') !== Map<ID,T>.get(1)

Sometimes we want to query the API for certain objects. We can now do
that by passing a URLSearchParams object to list operations.

All requestInit arguments could have been undefined already, because we
declared it as an optional argument, but sometimes it’s nice to
explicitly skip the argument with `undefined` which is now possible as
well.

Sometimes we don’t have a static list of choices but an async source for
them (like an API endpoint). This is now supported out of the box
through the searchProvider prop.

refs #185

refs #185

Bootstrap only displays form group errors if the .invalid-feedback
element is preceded by a .is-invalid element. That is an uncessary
restriction and we can simply enforce the errors to be displayed if it
is rendered.