Autoregistration of external providers

Currently we have two files containing providers we have in wink:

• META-INF/core/wink-providers - for core providers
• META-INF/server/wink-providers - for server providers

Currently there is an assumption that only one of above files exists and it will be loaded.
I think this assumption is ok, but I think we can provide additional feature of auto-registration of providers located in META-INF/wink-providers file.
So it should be enough to place wink-jettison-provider.jar in the classpath in order to load the jettison providers.

We'll also need property that will turn the auto-registration mode on/off, so the user can have a control over the providers.