db changes

created nw tables : domain_question, domain_answer (replacing
domain_posted_*), added capability support for both job and technology
(the one in technology is only for the test pushing algorithm, not to
be displayed in the app) and added a tracker of tested questions :
lkp_tested_candidate. Also some supplimentary support tables for tags
link.

The test generation system now should implement one metod
getTest(cand_id) - and use also technology, job types and capability
levels. Tests shoudl be pushed untill all available for a capability
level are exausted