Support basic auth, send API requests via proxy server

[nite-knite]

Replace the original server with a koa app.
All API requests will be sent to kong-dasboard server and then passed to appointed kong nodes.
New kong-dashboard server (optionally) supports basic auth itself (so that kong admin API can be set to only accessible locally).
Serve dashboard page at /dashboard since all requests (including GET /) will be forwarded to kong node.

[PGBI]

@NKCoding Thanks a lot for your contribution!

However I noticed the -p option doesn't work anymore:

# this still launches kong dashboard on port 8080:
kong-dashboard start -p 9000

Could you fix that?

[nite-knite]

@PGBI OK, I'll look into it.

[nite-knite]

@PGBI
Now it works and handles unsupported options and commands in a better way.
In the non-basic-auth mode, server respond with 400 rather than 500 when Kong-Node-URL header is missing.

[PGBI]

@NKCoding Sorry again for the time it took to merge. It's now done. Thanks for your contribution!

I did change some things:

• the proxy server was listening at "/" while the angular app was served at "/dashboard". I changed that to keep the current behavior: angular app is server at "/" while the proxy servers listens at "/proxy".
• If the Kong API was itself protected by basic auth, you needed to set the same name/password for the API and when starting kong-dashboard. Now you can protect Kong-dashboard with some credentials while having Kong API being protected with other credentials.