feature(server): Add a forwarding proxy for IE8.

* Proxy auth server requests when the url is prefixed with `/auth`
* Proxy oauth server requests when the url is prefixed with `/oauth`

fixes #102
The oauth tests pass locally but fail on travis:
> [2014-06-25T10:45:51.334Z] server.proxy.INFO: proxying request: (POST) /oauth/v1/authorization => http://127.0.0.1:9010/v1/authorization
[2014-06-25T10:45:51.336Z] server.proxy.ERROR: proxy error: Error: connect ECONNREFUSED
FAIL: #oauth server proxied POST request (11ms)
AssertionError: expected 500 to equal 400
at Request.<anonymous> (/home/travis/build/mozilla/fxa-content-server/tests/server/proxy.js:64:14)
at Request.<anonymous> (/home/travis/build/mozilla/fxa-content-server/node_modules/intern-geezer/lib/Test.js:98:15)
at Request._callback (/home/travis/build/mozilla/fxa-content-server/node_modules/intern-geezer/lib/Test.js:110:16)
at Request.self.callback (/home/travis/build/mozilla/fxa-content-server/node_modules/request/request.js:121:22)
at Request.EventEmitter.emit (events.js:98:17)
at Request.<anonymous> (/home/travis/build/mozilla/fxa-content-server/node_modules/request/request.js:978:14)
at Request.EventEmitter.emit (events.js:117:20)
at IncomingMessage.<anonymous> (/home/travis/build/mozilla/fxa-content-server/node_modules/request/request.js:929:12)
at IncomingMessage.EventEmitter.emit (events.js:117:20)
at _stream_readable.js:920:16