Up to now we have been treating the *first* class to be compiled
as the "main" application and adding @EnableAutoConfiguration. This
isn't always appropriate (e.g. if it's a test case), so now we
look for an appropriate annotation before falling back to the old
behaviour.
In addition ensures classes with a field of type Reactor trigger
the reactor auto imports.
See gh-969
JUnit tests can now be @SpringApplicationConfiguration
and @IntegrationTest without any explicit imports. Also
makes @RunWith(SpringJUnit4ClassRunner) optional.
Fixes gh-969
