Prevent cryptic exception if SecurityProperties not created

Previously if a user happened to provide an @EnableWebSecurity bean
the SecurityProperties would not be created, which is fine until you
add the Actuator (which needs them). Fixed by adding an explicit
SecurityProperties @Bean if not already present.
Upgrade Jackson
Add extra condition to security properties config
Allow default DispatcherServlet to be switched off more easily

All a user has to do now is declare a bean with name "dispatcherServlet".
Enabled JMX export auto configuration by default
Upgrade Spring
Document switching off DispatcherServlet
Prevent type not present exception when no security on classpath
Fix failing test due to change in JMX export default setting
Support for @Beans of type HttpMessageConverter, and Jackson specific details

You can contribute additional HttpMessageConverters
by simply adding beans of that type in a Spring Boot
context. If a bean you add is of a type that would have been included
by default anyway (like MappingJackson2HttpMessageConverter for JSON
conversions) then it will replace the default value. A convenience
bean is provided of type MessageConverters (always available if you
use the default MVC configuration) which has some useful methods to
access the default and user-enhanced message converters (useful, for
example if you want to manually inject them into a custom
RestTemplate).

There are also some convenient configuration shortcuts for Jackson2.
The smallest change that might work is to just add beans of type
Module to your context. They will be registered with the default
ObjectMapper and then injected into the default message
converter. In addition, if your context contains any beans of type
ObjectMapper then all of the Module beans will be registered with
all of the mappers.
Add test and fix bug in MessageConverters
MessageConverters -> HttpMessageConverters
Attempt to make URL comparison windoze proof
Update Spring Integration to 3.0
Readme updates for gradle plugin
Split MessageConverters auto config out into separate class
Avoid double logging config init + support for slf4j-log4j.
Add log4j starter and some documentation

As discussed in gh-162
Remove SystemProperties from tests in strict mode

Remove system properties when testing strict property binding. This
prevents test failures that can occur if the local environment happens
to have certain environment variables defined.
Rework HttpMessageConverters