Since there is no Heartbeat or InstanceRegisteredEvent when using the
SimpleDiscoveryClient we need to listen on the ApplicationReadyEvent
and register the configured instances

closes #505

In order to reduce the noise in the application log, only the first
failure when registering is logged on the WARN level. All further
attempts are logged using the DEBUG level.

closes #490

With this commit two new properties were added to ease the client
configuration when used in servlet containers:
`spring.boot.admin.client.management-base-url` and
`spring.boot.admin.client.service-base-url`. Both properties can be used
to specify protocol, host and port for the urls. The paths will still be
guessed and appended to the base-urls. Additionally the servlet context
path is not read from the properties but from the ServletContext itself.

closes #488

in order to get the ConfigurationProperties correctly recognized we need
to provide some getters for the properties.

fixes #493

In case there are multuple MessageConverters present, we mus make sure
that the message gets converted into json by setting the content-type
header to application/json.

fixes #445

fixes #489

fixes #479

fixes #477

With this commit all values from /metrics are shown and a option to
filter these values is provided

closes #264

Until now the thread querying the application endpoint can be blocked
for a very long time when the application is inresponsive. With this
commit two new properties `spring.boot.admin.monitor.read-timeout`
(default: 2s) and `spring.boot.admin.monitor.connect-timeout` (default:
5s) are added.

closes #462

Since the healthIndicator for Hystrix lists all discovered services, it
looks like the filtering is broken.  So we need to ignore the status
information when filtering the application list.

fixes #438

closes #439

Adds a workaround for
https://github.com/spring-cloud/spring-cloud-netflix/issues/1815
by including spring-cloud-context to the server's dependencies

A new property `spring.boot.admin.discovery.services` is added. It can
be used to restrict the services registered via discovery to a
whitelist (supporting simple patterns). Until now only blacklistin was
supported. The default whitelist permits all services.

Brings a fixed httpclient.

fixes #419