Change BETA banner for HMRC manuals

- Removed Slimmer beta label
- Added Slimmer template
- Included govuk_component template
- Added handling for different Beta Labels for HMRC and non HMRC manuals

Removed slimmer settings for beta banner and added in handling for different manuals (hmrc and non hmrc) to have different banner text

Trello ticket: https://trello.com/c/Z2z8wKgh/432-hmrc-manuals-frontend-3
1 more thing (sorry). Can you move this line to `app/views/manuals/_header.html.erb`? This way, this partial always gets called even if the manual isn't it beta. Moving it out would only call the partial if it's true.