fix: upgrade http-proxy module for bug fixes

[terinjokes]

The http-proxy module was significantly outdated, and was missing many
bugfixes to support node newer than 0.10, as we as a refactor and
simplification of their codebase.

This commit upgrades the http-proxy dependency, and refactors the proxy
middleware to utilize the new API.

parseProxyConfig (an internal function) now takes the proxy
configuration object and converts it into an array of "ProxyRecord"
objects, sorted by path. A ProxyRecord object contains:

• host The remote proxy host
• port The remote proxy port
• baseUrl The remote proxy path
• path The local URL path (that triggers the rewrite)
• https Boolean to determine if the remote connection will be made
  with SSL.
• proxy The instance of http-proxy.

This change was necessitated by the removal of http-proxy's
RoutingProxy API, and the desire to only create one proxy instance per
configuration item.

The middleware simply determines if the current request matches a known
proxy path, and calls the proxy's .web and .ws methods with the
current request and response objects.

The relevant unit tests were rewritten in light of these changes.

[megawac]

big 👍

[dignifiedquire]

This is great, a big thanks first of all!
There is only one question I have, what about the option proxyValidateSSL, why did you remove it?

[dignifiedquire]

Could you change this to ^1.11.1 please?

[dignifiedquire]

ping @terinjokes

[terinjokes]

@dignifiedquire sorry, i've been busy and didn't check in on this.

I no longer remember why I modified proxyValidateSSL, but I'll rebase this today and try to answer it for you. 👍

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[dignifiedquire]

Thanks

[dignifiedquire]

Merged as bcce563