Add frequency statistic to Terms

[TheVanadium]

Is your feature request related to a problem? Please describe.

If I need to memorize certain words, I'd like to memorize them in order of frequency so I am learning the most useful words. There isn't an obvious way to find the most frequent words for memorization.

Describe the solution you'd like

I want a new column in the "Terms" table with a percentage frequency of how many books the word appears in and/or a count of how many times the word has occurred across all books. This way, just like the other columns, we can sort by the value.

Describe alternatives you've considered

n/a

Additional context

The Terms table I'm referring to, where I would like the frequency statistic to be:

[jzohrab]

This is blocked by #532. That issue might be tough to implement reasonably, as it’s potentially a ton of data.

I’m not sure that this idea will be effective for learning. Common words will always show up, and there will be a pile of words in the middle that only appear a few times … one has to make a judgement call about what to work on, and maybe a calculated stat isnt a good guide. But I don’t know, and I can understand why this stat might be appealing.

Also needed: some way to indicate the overall stat for a family of terms, because there may be many different forms and combining would make sense.