Initial modelling of testcases and regressions, refactoring of kci API access

NOTE: These changes make run_tracker fetch regression data from the KernelCI API, making it much slower than simply gathering the data from the email reports, but good as a first step towards proper data modelling and to be able to link bisections to regressions. .gitlab-ci.yml is updated to use my own KernelCI API token for now.