Added a Vimeo EnableDNT privacy option to the Hugo config. This will enable the Vimeo 'Do Not Track' flag when either Vimeo shortcode tempalte options are used. When enabled, it will force the Vimeo player to be blocked from tracking any session data, including all cookies and stats.
Fixes#7700
Add an optional "title" attribute to the iframe in the vimeo shortcode. If one is not given, the title attribute will default to "vimeo video". It is imperative for iframes to have a non-empty "title" attribute in order to meet WCAG2.0 accessibility guidelines https://www.w3.org/TR/WCAG20-TECHS/H64.
Having them in separate files should make maintainance easier.
When adding new or making changes to the templates:
```bash
mage generate
```
This will get the Go code in sync.
Fixes#4457
