Gradle is easy enough to import into IDEs, so pom.xml should no
longer be necessary.
This commit removes the pom.xml files from the build.
Fixes gh-4283
This commit creates a UserBuilder and updates samples to use it. We do not
leverate it for JdbcUserDetailsManager because it requires the schema to
be created which is difficult with a single bean definition and
unpredicatble ordering. For this, it is still advised to use
AuthenticationManagerBuilder
Fixes gh-4095