Companion Bill Features [Epic]

This is the overall Epic ticket for the implementation of features re "companion bills",

**Context:** "Companion bills" are a common occurrence in the legislature, where the same bill is introduced in both the House and the Senate. The bill is given a Senate # and a House #, which move independently through the legislative process but often maintain the same text. It is common that advocates submit their testimony in reference to both bills. Users have told us it would be useful to be able to submit testimony on both bills with one process.

Goals: (and reference for design team)
1. When a user clicks through the testimony process of a bill that has a companion bill, somewhere in the process (perhaps on the 'thumbs' page), we ask the user if they would also like their testimony featured on the page of the companion bill.
2. When a user looks at the page of a bill (that has a companion bill), there should be some indicator and/or link to the page of the companion. This could simply be text that says "this bill has a companion bill. click here to see the companion page". Or we could have a checkbox that, when clicked, adds in new testimony from the other page and indicates which testimony is on both pages.

Back-end task: identify bills in the legislature that were introduced as "companion bills", and add a marker in the database.