Calculate the length of matched sections for the bill-to-bill page

[aih]

The 'similarity' between sections is related to the length of the section, and the amount of overlap. For the bill-to-bill page, it would be useful to show the length of each matched section. If possible, the length of the top 10 sections for each bill.

In a separate series of issues we'll look at creating a 'compare bills' page, which dynamically matches sections and compares them for both whole bills (not just the top 10, and not using Elasticsearch).

[aih]

Related to #85

[aih]

We no longer store the section_text. So this would require a recalculation of bill_similarity. It means that instead of the section text to calculate the length of the text and save that. E.g. 'This is the section text. It may be very short or very long'.length = 59

[aih]

Possible future enhancement. Not a priority at the moment.