Reduce loops for metatags in head

[MarauderXtreme]

I have identified three scopes where metatags can be defined.
List from broadest to narrowest:

1. "global" - general definitions, no i18n - reside in data/metatags.yml
2. "i18n" - definitions for i18n - reside in i18n/LANG.yml
3. "page" - definitions on page level, i18n and no i18n - reside in front-matter or defaults scope

To allow for overrides on narrower level I loop through every scope from narrow to broad and save the key to prevent overriding from broader scopes.

Since there are three general types of metatags (name, property, rel) I have created three includes accordingly.
To reduce loops it needs to be checked if merging of arrays is somewhat possible or implement it manually.
This helps to ease handling of special cases like og:image.