closes #627

In order to make the starters compliant to the spring boot naming rules
I added a codecentric-* prefix to the server and the client starters.
All samples are now using our starters and the docs were alignes with
these changes. In order to not suprise existing users I've added a
relocation to our old module

I removed the unecessary plugins from the build and reworked it to use
the ci friendly way of setting the version for releases (see
https://maven.apache.org/maven-ci-friendly.html).

This removes the spring-boot-starter-parent from the build, and
duplicates the necessary plugin configuration in he Spring Boot Admin'
parent instead. This way our BOM doesn't include version for
dependencies managed by boot's BOM

closes #597

This helps to quickly track down configuration problems, especially in systems that generate the config rather than depend on flat files.

closes #591

fixes #590

fixes #590 (old client - new server)

fixes #590 (new client - old server)

fixes #590

fixes #578

Options requests are now passed to the servlet. Therefore the
OptionsDispatchungZuulController isn't necessary anymore.
This fixes a memory leak introduced by this class.

fixes #545

fixes #531

fixes #515.

fixes #529

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