Integrate open_words into the DatabaseBridge mechanism

[blagae]

Use https://github.com/blagae/open_words to get the root of words being used, so that we can have better metrical data for declinable words and fewer verses with not enough information.

In practice, this means refactoring the WordOccurrence to either leverage open_words or be replaced by it. Also make sure to feed back that metrical data into open_words (or its handling code/db mechanism).