Started work on XML based IDM configuration

What I did is:
1) Created Java classes for types which are used to XML-Java mapping. For now, I added those classes into "picketlink/federation" module into package "org.picketlink.identity.federation.core.config.idm" .

Only reason to have them in federation is, that they need to be visible from class PicketlinkType, which is part of Federation module. (It was agreed that we will use big picketlink.xml, which will contain configuration of all picketlink components together). Seems that we need to extract some stuff related to XML parsing from federation module into config module, as currently "config" module is dependent on "federation" .

2) I've made STAX based XML parsing in config module. See IDMConfigParser and unit test IDMConfigParserTestCase

3) I've added some temporary reflection based hack to PicketlinkConfigParser, so it can instantiate IDMConfigParser from "config" module and use it. This needs to be fixed once we extract XML parsing stuff from "federation" module to "config" module (mentioned in point 1)

4) I've added class XMLBasedIdentityManagerProvider to IDM. It will be used to build IDM IdentityManager from parsed XML configuration. Not much work done here atm. I am planning to  use reflection based classes from IDM module to help with this.

Let me know if there are some questions/concerns around this.