Made BeanHelper a bean class.

Instances can now be created and configured in isolation.
BeanHelper provides a straight-forward implementation of BeanCreationContext
for interacting with the used BeanFactory.
Note that this commit breaks the build because there are still a bunch of
references to BeanHelper's static methods.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1520793 13f79535-47bb-0310-9956-ffa450edef68