This will allow us to use type annotations, lambdas, etc. Documentation
already states Java 8+ as a requirement.

Bulk deletes run by periodic clean ups might fail when run for the first
time or after and there are a lot of documents accumulated

Lists of documents for deletion are now partitioned into sub lists with
a maximum of 500 elements using Google Guava.

Stagemonitor and its dependencies are no longer included in builds. To
enable Stagemonitor in production, the libraries must be provided by the
host system. Additionally, the Java Servlet container needs to be setup
to load these additional dependencies for the web app.

For Tomcat 8 this is done by setting up a context config file in
conf/Catalina/localhost/<context path>.xml with the following content:

    <Context>
      <Resources className="org.apache.catalina.webresources.StandardRoot">
        <JarResources className="org.apache.catalina.webresources.DirResourceSet"
            base="<path to Stagemonitor JARs>"
            webAppMount="/WEB-INF/lib">
        </JarResources>
      </Resources>
    </Context>

See https://tomcat.apache.org/tomcat-8.0-doc/config/resources.html for
more configuration options.

The new version is required for upcoming changes.

The JavaMail API w/o implementation was accidentally used with an
upgrade of the Maven dependency.

This fixes a regression introduced in commit
0b0204e9.

Jetty 9.3 increases the JRE requirement to version 8.