[#8927] Add in click tracking to 'Start again' links

- https://www.agileplannerapp.com/boards/105200/cards/8927
- In order to understand our current usage on 'Start again' links in smart answers, we should set up and deploy event tracking on these links
- This should help us when making decisions relating to this kind of interaction in the future
Merge pull request #1371 from alphagov/feature/add-start-again-link-tracking

[#8927] Add in click tracking to 'Start again' links
Remove all references to 'undo' links

The original commit that added tracking to these links appears to have gone in in April as a temporary measure to support some design reckons. This commit proposes to take out the link tracking and css references to 'undo', as we no longer seem to have the concept of an 'undo' link in the markup.

Original ref from `git log -p -S 'This is short lived tracking'`:

```git
commit cfefadf12a3844bb03838b9b2d9cd98fe2239bb6
Author: David Singleton <david.singleton@digital.cabinet-office.gov.uk>
Date:   Mon Apr 28 13:38:39 2014 +0000
```
Register a Birth SA - FC update
Revert "Deploy Lost or Stolen Passport SA"

This reverts commit 723baf34359d14f599698e31908c76c83a4f9048.
Merge pull request #1373 from alphagov/revert_deploy_of_lost_stolen_passport

Revert "Deploy Lost or Stolen Passport SA"
Change getCurrentSlug to pass back more information

- Previously if we had a URL that was e.g. `http://smartanswers.dev.gov.uk/overseas-passports/y/afghanistan/applying` `getCurrentSlug()` would return `"overseas-passports"`
- Now from that URL we will return `"overseas-passports/y/afghanistan/applying"`
- This is based on a conversation with @antimega about the actual usefulness of what we're capturing. With this level of fidelity we capture not only that someone clicked on a link inside the `overseas-passports` flow, but the point in the flow that they decided to change their answer.
Indentation cleanup

- Not sure how this ended up over here, it shouldn't be
Use `getCurrentPosition` for start again, pass href for 'change answer'

- Adds click tracking back in for changing of answers.
- Tracks the href of the change answer link in its entirety, e.g. `"/overseas-passports/y/?previous_response=afghanistan"`
Marriage Abroad SA - Content update
Merge pull request #1377 from alphagov/update_marriage_abroad_home

Marriage Abroad SA - Content update
Merge pull request #1375 from alphagov/feature/change-link-tracking

Add in link tracking for 'Change Answer'
Deploy Marriage Abroad SA
Merge pull request #1378 from alphagov/deploy_marriage_abroad

Deploy Marriage Abroad SA
Remove need for silence_warnings in tests

Specify flow registry options as an optional parameter for
instantiation
Fix SmartdownAdapter::Presenter test

The answer used was invalid since the question in the flow is a yes/no multiple choice question, not a date
'Register a Birth' in Smartdown and comparison tools
Content changes following first comparison run
Run smartdown scenarios in rake tasks
Move automated task helpers to Utils, reorganise question-specific rake tasks