Added support for Nested Properties

Hi Tommi. I've made some changes on the LQC.
When you have time, please look if this patch is OK for inclusion.

Tips are wellcome :)

- Support added for EntityContainer and LazyEntityContainer
   - Based on the CompositeItem structure
 - Small refactory adding an AbstractEntityContainer
   - Moved redudant code present on Entity and Lazy Entity Containers
   - API for management of Nested Properties
 - Modified EntityQuery and EntityQueryDefinition to parse and add
   nested properties using the EntityNestedProperty implementation.
 - Added Unit tests for EntityNestedProperty implementation.