closes #201

fixes #202

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

fixes #184

fixes #175

added CompositeNotifier to allow for multiple notifiers. Only used when multiple notifiers are configured and no primary notifier is already configured.

Chrome dosesn't send parallel requests for the same url. To circumvent that
behavior add a dummy request-parameter to the event-stream url. Otherwise
the journal section shows no content on chrome while doing the sse long polling

Fixed HipchatNotifierConfiguration to be a static class

changed HipchatNotifierConfiguration to be a static class, otherwise application context doesn't start up when hipchat notification is enabled.

If the management.port and server.port is not the same, the current logfile-
endpoint detection fails. With this commit the presence of the endpoint is
determined via a HEAD-request

fixes #165

This commit contains multiple changes:
 - Start the registration task after the ApplicationReady event. This makes
   AdminClientProperties.isReady() unnecessary.
 - The RegistarApplicationListener has two new public methods to start/stop the
   periodic registration task.
 - Add spring.boot.admin.auto-registration property (default: true). When this
   property is set the registration task is automatically scheduled after the
   ApplicationReadyEvent.

closes #151

The RemindingNotifier sends periodic notifications using a delegate. It must be
added explicitly to the ApplicationContext

This commit enables the use of // @formatter:off and // @formatter:on
to surround lines of code that should not be formatted.

In case prefer-ip is true and no server.address is set use the IP address from
InetAddress.getLocalHost(); like it is done in Eureka.

When an empty application list was initially returned the events wasn't  pushed
into the applications array, because the Applications.query returned no array.
This issue made a page refresh necessary.

Add spring.boot.admin.client.enabled property to explicitly disable the
spring-boot-admin-client, (e.g. for unit tests). Defaults to true. The client is
active when spring.boot.admin.client.enabled is true and spring.boot.admin.url
is set.

fixes #156

The polling in the UI is replaced with server side events. Status changes are
now reported immediately from the admin server to the UI.