Clean up schemas

- Turn class methods into functions, following CKAN style and common sense
- Remove unused imports
Move metadata quality function to helpers

This might be a more natural place for a function that's
supposed to be called from templates, and it also helps avoid
a circular import in further work on metadata quality indicators.
Indicate metadata quality with circles instead of stars
Wrap schema methods within a class

This allows them to be reasonably called as actual class methods.
Fix import error
Show metadata quality indicator in search results
Display the metadata score in search results less prominently
Fix translation broken in previous commit; minor tweak
Clearly indicate in UI that the quality indicator is for metadata

Just a visual indicator alone could easily be mistaken to be a quality
rating for the data itself, so make it clear in the UI that it's about
metadata completeness, not a rating for the dataset.
Align the metadata rating in search results better
Merge development back into branch 564-meta-quality-indicator-improvements
Fix tests to reflect refactored utils/helpers code