Fix issue where the Hystrix dashboard will not load

Overrides Spring Boot's FreeMarkerAutoConfiguration to prefer using a
SpringTemplateLoader instead of the file system. This corrects an issue
where Spring Boot may use an empty 'templates' file resource to resolve
templates instead of the packaged Hystrix classpath templates.

When creating a new project with Spring initializer, an empty
'templates' resource directory is automatically added to the new
project, causing a scenario where this issue may occur.