fixes #477

Added documentation and a sample on how to secure the SBA-Server and
leverage the new login ui-module

closes #361

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.

As now with spring boot 1.4 there is a special goal for generating the build-
information, we use it for displaying the version in spring boot admin. The old
info.version property still works but is deprecated. From now on
build.info.version is taken into account.

With this commit urls form the /info endpoint are deteceted and rendered as
links.
The downside is to make that work I had to drop the collapsible info section in
the overview list and replaced it with an resizable/scrollabe <pre> section.

This adds a new FilteringNotifier which can use filters to suppres certain
events from being notified of. Two filter implementation are provided, one
filtering by name and one by id. Additional when a FilteringNotifier bean is
present, the autoconfiguration creates a REST-controller to add and remove
filters at runtime.

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

remove logfileEndpoint
rename logback.xml to logback-spring.xml in samples

fixes #98

fixes #61

To enable, you just have to add a DiscoveryClient to your Spring Boot Admin Server.
Also did some code polish.
Closes #44