Bring tabs component in line with Nunjucks macro

[peteryates]

This mostly makes the tabs component work like the original Nunjucks macro.

The one difference is that because here we're generating the tab ids based on the title label, there's no real need for idPrefix.

Providing the user doesn't have two tabs with the same name, the ids will be unique.

Changes

• Stop using matcher now we're using the tag helper
• Allow the tabs component to take a custom id
• Rename the tab slot's title to label
• Allow tab text to be set via arg as well as block