Filter out duplicate section matches in bill-to-bill

[aih]

Related to #85

If both the from and to section match, de-duplicate. It's expected that some sections will match more than one other section, e.g. 1 => 2, and 3 => 2), and we do want to display those.

[aih]

Duplicates in a0a360f due to different versions of the right-side bill. In the display, these can be collected into one row, and add one column for 'Version'. In that Version, column, here, for example, we'd have ', IH, EH, RH' (with '' for none). This is because section 1 of 114hr2209 matches section 2 of 115hr1624 four times, for different bill versions.

Edit: this comment has been added to a new issue

[aih]

Fixed in 71e407