Increase priority of EndpointHandlerMapping

The Actuator endpoints ought to take precedence over others (since
they are important and users can isolate them using management.contextPath
if necessary). This change puts the @Order at -100 (well before the default
order of the RequestMappingHandlerMapping at 0).

Fixes gh-1107
Add @Conditional to prevent HATEOAS blowing up

Spring Plugin is required when using @EnableHypermediaSupport
Add @EnableEntityLinks to hypermedia support
Add @Conditional to prevent HATEOAS blowing up
Grab main class from "run" task if it exists

The test is a bit crap at the minute (no assertion), but the build
is successful and you can see from the log that the correct main
is used

Fixes gh-1099