Add auto discovery capacity to circushttpd.

Now circushttpd will try to discover circusd endpoint in
local area network on start and show them on connect page.

Always show textinput in connect page as well as the endpoint select box.
Do not show endpoint select box if no endpoints has been detected.
If no endpoint selection, use the textinput value with the default value
set to tcp://127.0.0.1:5555.