Fixes gh-1205

This commit resolves an issue where some versions of Cloud Foundry are
setting the 'Connection: close' HTTP header in the Hystrix stream
response, which causes the dashboard to not display the stream data.

See https://github.com/cloudfoundry/gorouter/issues/71

fixes gh-204

When running from /hystrix or from / (with a forward) the
webjars and the monitor endpoint need to be resolvable, so
we need to use the FTL macros again.

Fixes gh-193

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.

I didn't see a way to do this without dynamic rendering, so
now we have a freemarker dependency (not huge I guess).

Fixes gh-51