Since a HEAD request to the heapdump triggers a dump we need to test the
availability of the heapdump endppoint via OPTIONS-request.
To get this working we need to ensure that the OPTIONS-request are dispatched
to the zuul servlet as this wasn't done prio to this commit adding the
OptionsDispatchingZuulController.

fixes #226

From Spring Cloud Brixton on, the PreDecorationFilter doesn't pass sensitive
headers downstream.
So the ZuulProperties from the ApplicationContext needs to be used (instead
of creating a new instance), so that the properties can be customized.

Update to Spring Cloud Brixton and add the concept of ServiceInstanceConverters.
A ServiceConverter is used to convert discovered ServiceInstances to
Applications. The old converter and one for Eureka is provided. It is also
possible to provide your own implementation.

closes #154

Cause it was often requested, now the context-path for the admin server is
configurable. This allows to move the admin-ui and endpoints to other http-
paths than "/".
NOTE: I'd still advise not to add the admin to the application you want to
monitor.

Deriving from Spring Clouds ProxyRouteLocator has become too difficult. It would
have required to either set fixed ZuulProperties or providing a DiscoveryClient.
So we are shipping our own lean version of it. Since the PreDecorationFilter is tightly
coupled to the ProxyRouteLocator we also have to use our own stripped down version.

closes #123

 * Use @EventListener instead of ApplicationListener-interface
 * Don't inherit ClientApplicationEvent from ApplicationEvent - so JournaledEvent isn't needed anymore
 * added eclipse formatter rules
 * reformatted all files