Fix spring transaction support and correct the transaction hook location in the example spring-txn

The glue path in ```@CucumberOption``` annotation of the RunCukesTest in the spring transaction example, was not updated when the SpringTransactionHook class was moved from cucumber.runtime.java.spring.hooks to cucumber.api.spring. Therefore the example is currently actually a "spring-without-transactions-example".

The root cause is that there will be two separate spring contexts, one based on ```cucumber/runtime/java/spring/cucumber-glue.xml```, and one based one the ```@ContextConfiguration("<cucumber.xml>")``` annotation. SpringTransactionHooks will be in the first context, and the step definition class (with the ```@ContextConfiguration``` annotation) and the application under test will be in the second context.

A "hack" to make the spring transaction support work is to let the cucumber.runtime.java.spring.SpringFactory "detect" the ```@ContextConfiguration``` annotation on the step definition classes and apply that configuration also to the SpringTransactionHooks

Fixes #637.