Fix compare task and remove common flase-errors

- Transition flows now have '-transition' appended, by convention,
  which means the flows don't share the same slug. Update the helper
  to be aware of this and pick the non-transition flow to compare
- Remove some false positive diffs:
  - Exclude sidebar, breadcrumb and analytics content from diff, as
    only the non-smartdown flow will have a real sluf, with related
    content for those areas
  - hide the '-transition' URL differences
Strip trailing new lines from yml-govspeak input

This was causing false-positives in the Smartdown transition
comparison tool, where YML content had (many) extra trailing
new lines.

They should be non-content affecting, so this won't
change any rendering behaviour, but will normalise the output
Upgrade Smartdown

This fixes a bug with previous question page titles and
removes some variable whitespace that was causing false
positives in the compare task
Merge pull request #1149 from alphagov/fix-smartdown-compare-task

Fix smartdown compare task