Move to BaseRunner hooks architecture
    
    This starts moving repository hooks over from a set of symlinks into
    the git repos' hooks/ folder into the files over to a Runner class
    per plugin.
    
    This requires less constant meddling with files, and allows a single
    hook to perform multiple tasks at the same time.
    
    To do after this is changing lib.git.TemporaryClone.runhook to call
    run_project_hooks and removing lib.repo.PagureRepo.run_hook.
    Also to do is migrating the rest of the in tree hooks over to the
    Runner architecture.
    
    Signed-off-by: Patrick Uiterwijk <patrick@puiterwijk.org>