Extract Judge::get_problem_sources
Fix and open-code unsupported_DEs
Extract Judge::delete_req_details
Extract Judge::insert_req_details
Extract Judge::get_problem_tests
Extract Judge::get_problem
Extract Judge::is_problem_uptodate
Select run_all_tests together with the request
Use Judge::get_problem in initialize_problem

Main module does not depend on CATS::DB any more.
Extract Judge::Config
Extract Judge::Log