This PR introduces a basic AdminNotice model to store these notices. Admin notices are categorized by their source/type (currently only notices from problem check.) They also have a priority.
Doing the following renames:
Jobs::ProblemChecks → Jobs::RunProblemChecks
Jobs::ProblemCheck → Jobs::RunProblemCheck
This is to disambiguate the ProblemCheck class name, ease fuzzy finding, and avoid needing to use :: in a bunch of places.