I can get a list artifacts that matches my selected criteria

- Create a report that will display all open bugs in a release (the bugs are contained in sprints which belong to a release)
- Create a report that will display all open bugs in a sprint
- Create a report that will display all test cases in a sprint
- Create a pie chart by status of all test cases in a sprint

There are many more scenarios. Listed above are just a few


Initial spike already carried-out.

- Resulting "poc" code here: https://tuleap.net/plugins/git/index.php/101/view/134/?p=spike_linked_artifacts_from_agile_search.git&a=blob&h=44d80cbf098e61203214a87c7d820aa72f7dfaf1&hb=184f07363a83aa61afd8e0a41f761927315a46b3&f=plugins/agiledashboard/include/BigSearchDao.php

-Notes:
* The general theory is to determine the best path between ,say, a release and the associated tasks. To get this we analyse the existing hierarchies to which the release and tasks belong, respectively, and all existing plannings between them.

* The code will need to fit-into the existing search criteria format, i.e. need to create a block of "joins" and a blcok of "wheres".
@see Tracker_FormElement_Field::buildMatchExpression()
@see Tracker_FormElement_Field::fetchCriteriaValue()

* Cannot use HierarchyFactory for performance and reliability reasons.