[iso.qa] "Suggest a case for me"

Add a feature where the ISO tracker suggests tests for each tester to start on. This could either be a 'Feeling lucky' button, or perhaps a portlet on the left with 5 suggestions customised to that user.

The suggestions should be made using a set of heuristics and where possible be based on information the user has recorded in user prefs:

 * Available archs: [ ] i386 [ ] amd64 [ ] lpia
 * Other: [ ] LTSP setup [ ] DVD capable
 * Level: [ ] Beginner [ ] Seasoned tester

The system will try to pick the tests that need testing first (perhaps that typically get left to last) based on your arch and skill level (gives Ubuntu Live to a beginner) and expert mode to others, etc.

We might also consider changing the test case subscription system from being linked to the ISO, not the test cases and have it be a pure image notification service, rather than a case coverage tool.