Update data-module on layout header and footer

[danacotoran]

What

Change value of data-module attribute to "gem-track-click" on the layout header and layout footer components.

Why

The reason behind this change is that click tracking is not working on these elements on GOVUK Accounts.
That is because Accounts does not use static and therefore also does not use the track-click script which enables click tracking on modules with the data-module="track-click" attribute.

Changing the value of this attribute to "gem-track-click" means that the header and footer will work with the component gem's track-click script instead.

https://trello.com/c/9A6UPqi8

[alex-ju]

We already have this in lib and planning to remove it from static very soon https://github.com/alphagov/govuk_publishing_components/blob/master/app/assets/javascripts/govuk_publishing_components/lib/track-click.js

[danacotoran]

Yeah you're right @alex-ju.
Andy suggested that we should copy the old track-click module from static as he thought that the gem's version would not work as it's a re-written version of the old one.
However, I tested this locally by changing the data-module attribute to "gem-track-click", and that does seem to do the trick.

[alex-ju]

Thanks for looking into this, @danacotoran! That's great news! This is how we actually ended up with the current version in lib (by copying it from static), so I'd really like to avoid doing this again.

[alex-ju]

Don't forget to add a changelog entry.

We'll have to do this for every component, unfortunately, before being able to remove the copy in static.