This is a follow-on from the changes made in 2b7bf3e7. In addition to the
problematic use of @ConditionalOnClass that was addressed in 2b7bf3e7,
JerseyAutoConfiguration also used @ConditionalOnBean referencing a 
Jersey class. This has the same problem when used on a class that
implements WebApplicationInitializer. Implementing
WebApplicationInitializer causes the class’s annotations to be
introspected during servlet container initialiser processing. If a
@ConditionalOnBean annotation references a Class that cannot be
loaded an ArrayStoreException occurs.

This commit updates JerseyAutoConfiguration to reference ResourceConfig
as a String. This allows it annotations to be introspected without
attempting to load a Jersey class that may not be on the classpath.

Fixes gh-1733
Fixes gh-1719