Modernize James configuration

Apache James currently relies on commons-configuration, and thus on XML configuration files.

As such the configuration process has several problems:

• Working with XML is boiler plate
• Working with file leads to a real lack of flexibility.
• For instance, in a cluster environment, we would like all the James server to share the same configurations.
• Also, in tests, we need to test the different configuration values. We can not do this without overwriting files, which is dangerous, and boilerplate.

What we need is:

• To represent all possible configuration via java objects.
• Configuration providers should be able to convert the configuration stored into the java configuration object.
• We should be able to inject different configuration providers from guice/spring.

It would allow to specify alternative configuration backends (different formats, different storage techniques) and allow direct injection (for tests for instance).

Here would be the steps for this work:

• Add a Initializable class in lifecycle-api. This should be called by Guice and Sprint at initialization
• configure in Configurable will save a Java object (parse the HierachicalConfiguration into a java object representing it's content). Initialization will then be done by Initializable.
• Then we can move away, object by object, from the Configurable interface: We need to move the configuration parsing in a separated class (behind an interface). We can register ConfigurationProviders, with an XML/commons-configuration default implementation.
• Deprecate Configurable.
• Provide alternative configuration providers, for example, a Cassandra stored configuration provider