Add update-in-progress alert to sidebar of all regulation pages

[niqjohnson]

Show the update-in-progress alert from #843 in the sidebar of all pages of an affected regulation instead of just the landing page.

Additions

• Add new alert-in-a-sidebar styles
• Add new alert-in-a-sidebar Backbone view (and test)

Changes

• Pull the text of the update-in-progress alert into its own template since it's now reused across many page types
• Use label_id instead of reg_part in the reg_updates.py template tag (label_id is available in every template, reg_part isn't)
• Add the update-in-progress alert to all the relevant sidebar templates

Testing

1. Rebuild the frontend assets from this branch with ./frontendbuild.sh
2. Start eRegs locally from this branch (EREGS_API_BASE=https://www.consumerfinance.gov/eregs-api/ ./runserver.sh if you're running eRegs inside of cf.gov; EREGS_API_BASE=https://www.consumerfinance.gov/eregs-api/ python manage.py runserver if you're running it standalone).
3. Pop on over to eRegs at http://localhost:8000/eregulations/ and go to a reg that has updates in progress. Reg B (1002) is a good candidate since it has every page type that the new alert will appear on.
4. Verify that the update-in-progress alert appears in the sidebar on every page type in the reg as shown in the screenshots below:
   • Regulation text
   • Appendicies
   • Interpretations
   • Section-by-section analysis (1002.4 has SxS if you need an example)
   • Diffs
   • Search results

Screenshots

Reg with no SxS	Reg with SxS	Reg with definition	SxS	Diff	Search

Notes

• As seen in the "reg with definition" screenshot above, definitions will appear on top of the alert. That's intentional but not ideal (always keeping the alert on top of definitions would have required too many changes for the scope of this PR).
• The alert doesn't consistently appear on the search results page, but I think that's a bug with the search results page template and not with the alert (the help module doesn't always appear either, even on production). Given that you'll still see the alert on any page you get to from the search results page, this is again intentional.

[niqjohnson]

@higs4281: Ah, sorry, I think I forgot a step in the instructions. Since this touches some JS, try rebuilding the frontend assets with grunt build before you start the server (I updated the original PR comment to add that step).

[contolini]

The alert doesn't consistently appear on the search results page, but I think that's a bug with the search results page template and not with the alert (the help module doesn't always appear either, even on production).

Good find. I'm going to dig into this a little bit.