refactor and introduce without server configure option

Move server-only stuff into their own files and make building
that depend on not having --without-server on the configure

Make fragments in other places conditional as well

Remove client-related members from struct libwebscket when
building LWS_NO_CLIENT

Apps:

normal: build test server, client, fraggle, ping
--without-client: build test server
--without-server: build test client, ping

Signed-off-by: Andy Green <andy.green@linaro.org>