The Zuul filter registry has to be cleareed (including a cache in
a private field in FilterLoader, yuck).

With this change users can elect not to install the proxy features
but still have a Zuul server with @Beans of type ZuulFilter added
automatically.

Fixes gh-104

 fixes gh-105

fixes gh-76

fixes gh-98

Ribbon and simple host reverse proxy now share quite a lot of
code (everything to do with headers).

Fixes gh-103

Fixes gh-103

removed circular dependency between EurekaClientAutoConfiguration and EurekaDiscoveryClientConfiguration that caused DiscoveryClientConfigServiceBootstrapConfiguration to fail.

fixes gh-99

If user adds auth.route.<service>.scheme: passthru then instead
of adding the bearer token the filter will not do anything
(and the normal authorization header will be passed through
to the backend)

See gh-19

See gh-51

basePath should always be /contextPath/servletPath/ (the last slash being the location of the eureka dashboard)

fixes gh-101

fixes gh-100

Without this change the health status is always UNKNOWN because it
never finds the servo metrics for the health indicator. It's also
a general spruce up of the servo and eureka metrics and health
infrastructure which was looking a little more complicated than
it needed to be (no need for a separate MetricReader).

To avoid possible NPE when the registry is used before it is initialized.

Fixes gh-97

Conflicts:
	spring-cloud-netflix-core/src/test/java/org/springframework/cloud/netflix/feign/SpringDecoderTests.java

Using Spring as an object factory to control the lifecycle of ribbon clients.
So far we have a single, parameterized configuration class for all clients, but
can be extended to allow user to supply additional configuration. The current
model for user extensions is

@EnableRibbonClient(@RibbonClient(name = "foo", configuration = FooConfiguration.class))
public class MainConfiguration {
    ...
}

So in this example, MainConfiguration is part of the "main" application context
and FooConfiguration is used to create the Ribbon client and load balancer for
the "foo" service.

Document FeignClient

fixes gh-91

fixes gh-85

fixes gh-87