Update MongoDataAutoConfiguration to provide easier configuration of
CustomConversions, the MappingMongoConverter, MongoMappingContext
and an authentication database.
Fixes gh-1619
Fixes gh-1730
Switch the Tomcat 8 and Jetty 9 samples to Tomcat 7 and Jetty 8. Since
Tomcat 8 and Jetty 9 are now the default versions the previous samples
are no longer relevant, however, we do need integration tests to check
that we remain compatible with Tomcat 7 and Jetty 8.
See gh-1832