The page images selection order as follows:
1. Page's images parameter, image resources are supported.
2. Page's image resources that naming in *feature*, *cover* or *thumbnail* pattern.
3. If no page images specified, then the first one of site's images will be used as the fallback, supports site resources.
* Fix: updated date logic in opengraph template
* Updated date logic in schema template
* Reformatted opengraph and schema
* Wrapped PublishDate and Lastmod in with
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