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

fixes #395

With this change it is possible to include credentials in the instance
metadata which will then be used to access the client endpoints using
HTTP Basic authorization.

closes #359

With this commit you can now associate your applications with custom
metadata using `spring.boot.admin.client.metadata.*` sensitive values
are recognized by key and are masked in the http interface.

This can be useful in the future if there are instance specific settings
which should be used by the admin server, e.g. custom notification
recipients.

For now there is no extra imetadata view in the ui. The values are shown
in the environment view.

With this commit the concept of an ApplicationFactory is introduced.
This allows you to easily modify the information used to register
your application at the admin server

closes #331

Add support for the /loggers endpoint from spring boot 1.5.x. With this
change log4j2 (and every other logging backend supported by spring boot)
is supported in the logging view.
The old implementation will be kept a while, so that the clients aren't
forced to migrate.

closes #305