ISPN-3125 Applying Spring configuration from file with overrides

Hi

This is proposed fix of https://issues.jboss.org/browse/ISPN-3125 based on Mike's initial proposal: https://gist.github.com/MikeN123/5618297. 

I'm a bit unsure about adding setters to ConfigurationBuilderHolder. I had to remove final from fields, so it looks like it was designed to be immutable at the very beginning. If we want to limit immutability, I guess we should create another constructor and pass Global/Default configuration builders from ParserRegistry. However this way we'd add another dependency from ParserRegistry to Global/Default Configuration Builders.

Please tell me what's your opinion on that case.

Thanks!
Sebastian
Instead of these setters, did you try doing this instead?

```
configurationBuilderHolder.getGlobalConfigurationBuilder.read(gcb.build())
```

What ^ does is take the base configuration objects that you read from XML and override them with whatever `gcb` contains. Is that what you're trying to achieve?