This is an Element project (in the vector-im repo) so the Copyright
should be for New Vector: it was incorrectly attributed to the
foundation for some files (and some files were missing headers).
We only ever used the static instance() method to get to the config
object, so just make a static instance that returns the ConfigOptions
directly, throwing an exception if it's not yet initialised. This way
the types can all be non-optional (plus it's shorter).
