Add ErrorWrapperEmbeddedServletContainerFactory for error pages in WARs

Error pages are a feature of the servlet spec but there is no Java API for
registering them in the spec. This filter works around that by accepting error page
registrations from Spring Boot's EmbeddedServletContainerCustomizer (any beans
of that type in the context will be applied to this container).

In addition the ErrorController interface was enhanced to provide callers
the option to suppress logging.

Fixes gh-410
Update to Spring Security 3.2.1

Also change strategy for defaulting of Authentication. Spring
Boot authentication defaults are now encapsulated and can easily
be overridden by a user defined AuthenticationManager.
Fix tests

Some assumptions were being made in tests, e.g. about
there being an AuthenticationManager @Bean, which were
false with the new Security 3.2.1 updates from Rob.

Also parent-child contexts with the actuator were
problematic because they didn't exclude the web configuration
for the management security in the parent context.

Fixes gh-244
Add method security web sample

Useful sample for common use case where user adds custom Authentication,
a form login, *and* global method security all the the same application.
Add actuator to method security sample
Be defensive with auto-config of Servlet 3.0 features

There's no explicit support for older Servlet specs in Spring Boot,
but we can at least make it easy for others to provide such
support by not adding stuff to the context when in an older container.
Polish
Drop getPort from ConfEmbServletContainerFactory

Remove getPort() from ConfigurableEmbeddedServletContainerFactory to
keep the interface primarily setters.
Tweak ConfigurableEmbeddedServletContainerFactory

Update ConfigurableEmbeddedServletContainerFactory to no longer directly
extend EmbeddedServletContainerFactory.
Tidy ConfigurableEmbeddedServletContainerFactory

Rename ConfigurableEmbeddedServletContainerFactory to
ConfigurableEmbeddedServletContainer and extract
AbstractConfigurableEmbeddedServletContainer from
AbstractEmbeddedServletContainerFactory.
Rework ErrorWrapperEmbeddedServletContainerFactory

Rename ErrorWrapperEmbeddedServletContainerFactory to ErrorPageFilter
and extend AbstractConfigurableEmbeddedServletContainer rather
than AbstractEmbeddedServletContainerFactory.

Fixes gh-416
Correct link to samples.

Fixes gh-415