Small changes to improve readability

the combination of variable names, negation and unless
made it hard to read the rules for showing disabled
progress buttons.
Clear scheduled jobs on edition publish

if an editor choosed to immediately publish a
scheduled edition, we should clear the scheduled
sidekiq job. missed this when we implemented scheduling.
Merge pull request #254 from alphagov/clear-scheduled-jobs-on-publish

Clear scheduled jobs on edition publish