Add support for cache manager auto-configuration that is triggered when
the `EnableCaching` annotation is added to a Spring Boot application.

A new "spring.cache" set of configuration keys is also provided. The
"spring.cache.mode" allows the user to specify the cache provider that
should be auto-configured. If no explicit configuration is provided,
the environment is checked for the best suited cache implementation,
that is:

- Generic if at least one `Cache` bean is defined in the context.
- Hazelcast if either a default configuration file is present or the
  `spring.cache.config` property is set.
- JCache if one JSR-107 provider is present
- Redis if a `RedisTemplate` is defined in the context
- Guava
- Simple as a fallback option, using concurrent maps
- NoOp (that is, no cache) if the mode is set to "none"

If the provider supports it, it is possible to specify the caches
to create on startup via `spring.cache.cache-names`. If the provider
relies on a configuration file and a custom one needs to be used
`spring.cache.config` can be set to such custom resource.

If more than one JSR-107 provider is present, it is possible to force
the provider to use by setting the mode to `jcache` and specifying the
fully qualified class name of the CachingProvider to use via
`spring.cache.jcache.provider`.

See gh-2633

Closes gh-2376

SmartApplicationListener has been superseded by GenericEventListener as
of Spring Framework 4.2. It will be eventually deprecated and removed.

Migrate our event listeners to use the new contract.

Closes gh-2576

Update MailHealthIndicator to use the new testConnection() method
available as of Spring Framework 4.2

Closes gh-2666

When configured with a context path of "", Undertow 1.1.3 changes the
context path to be "/". The change [1] was made to fix UNDERTOW-350
[2].

[1] https://github.com/undertow-io/undertow/commit/3db7707b8b34095d8d2fafecf94a10d101c62320
[2] https://issues.jboss.org/browse/UNDERTOW-350

See gh-2732

Closes gh-2670

Conflicts:
	spring-boot-dependencies/pom.xml

Closes gh-2732

Closes gh-2730

Closes gh-2731

Conflicts:
	spring-boot-dependencies/pom.xml

Conflicts:
	spring-boot-dependencies/pom.xml

gh-2735

Closes gh-2733

Closes gh-2729

Closes gh-2734

Conflicts:
	spring-boot-dependencies/pom.xml

Closes gh-2726

See gh-2718

Closes gh-2718

Previously, the ErrorPageFilter was not invoked for async dispatches.
This meant that an error that was set during an async dispatch would
go undetected and a 200 response with an empty body would be returned.

This commit updates ErrorPageFilter to configure its
OncePerRequestFilter so that async dispatches are filtered and the
correct error handling is performed.

Closes gh-2711

Remove unwanted System.out.println call

Conflicts:
	spring-boot-dependencies/pom.xml

Closes gh-2702

Update SpringApplicationContextLoader so that the MockServletContext
uses FileSystemResourceLoader. This allows `/src/main/webapp` folder
to be found.

See gh-2654

Previously, SpringBootWebSecurityConfiguration required a web
application and @EnableWebSecurity to be on the classpath.
@EnableWebSecurity is in spring-security-config so this could lead
to the configuration being active when spring-security-web isn't
on the classpath but the rest of Spring Security is.

This commit updates SpringBootWebSecurityConfiguration to also make it
conditional on a class in spring-security-web.

Fixes gh-2717