Since the principal not necessarily is json-searializable we need to
avoid this and just pass the wanted properties to thymeleaf

fixes #799

closes #792

Everythind that looks like an http(s) url will be rendered as hyperlink
and ansi-color escapes are now supported.

In order to have ansi-colors in the file output you need to set a custom
pattern. e.g.:
logging.pattern.file="%clr(%d{yyyy-MM-dd HH:mm:ss.SSS}){faint} %clr(%5p) %clr(${PID}){magenta} %clr(---){faint} %clr([%15.15t]){faint} %clr(%-40.40logger{39}){cyan} %clr(:){faint} %m%n%wEx"

closes #670

fixes #785

Using spring.boot.admin.ui.title/spring.boot.admin.ui.brand you can
customise the page title and logo/title shown in the navbar

closes #212

Add a page with extra button to trigger a heap dump.

closes #734

server.servlet.contextPath set

The caches.size metric is not available for every cache implementation.
If the metric is not available the ui should still show hits and misses.
This commit ignores errors for the cache size and will do no further
requests for this metric after an error occurred.

fixes #756

also fix table styling in httptraces, auditevents and sessions

fixes #728

closes #697

The system.load.average.1m metric is not available on all platforms.
Therefore we ignore errors from fetching it.

closes #697

If the build version of the instance is present in the metadata it's now
also considered and the version is now a attribute on the instance
itself. So when using non-boot application they can provide it via the
registration metadata.

- use MimeMessage with Content-Type text/hmtl
- use a single template for subject and body
- use a Spring aware TemplateResolver