Fixed the NPE in in SpringTransactionHooks by turnign it into a Spring bean.
Got a NoSuchBeanDefinitionException instead.
````
org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [org.springframework.transaction.PlatformTransactionManager] is defined
  at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:295)
  at cucumber.api.spring.SpringTransactionHooks.obtainPlatformTransactionManager(SpringTransactionHooks.java:65)
  at cucumber.api.spring.SpringTransactionHooks.rollBackTransaction(SpringTransactionHooks.java:60)
  at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  ...
````

Relies on the #644, #637 issues.