Iterate on the data model of checks

Most importantly break up Check into CheckRun and CheckResult.
While creating wireframes and mocks we have realized that we want to
treat runs and results in a substantially different manner, so it felt
increasingly artificial to try and model them with the same entity.

We had already clearly separated checks into 6 categories, 3 of which
were run related and 3 were result related. So breaking this up does
not change that much, but makes the two different entities a bit
clearer, e.g. by removing `tags` from runs and only allowing one link
per run, and by removing the timestamp attributes from results.

Change-Id: Id60f7c2abcdf0304d9799cf9e6435b19f4372976
1 file changed