Updates behavior of sequence navigation menu

Another step in [#51593657]. This makes all the activity links in the menu change the "active" activity, i.e. the one with the blue highlighting and the visible list of pages. Final step should be to get this behavior with the carets/arrows and the previous behavior with the text links.

https://www.pivotaltracker.com/story/show/51593657
Nav menu: caret opens page list, activity name is link

[#51593657]

https://www.pivotaltracker.com/story/show/51593657
Assets and CSS to support HAS footer

[#54535284] The HTML in `/docs/has-footer.html` actually needs to be put in the Project object describing the project. (I'll do that on staging and production when this gets deployed to those servers.) Logos, as of this commit, are just laid out at the bottom of the footer box.

https://www.pivotaltracker.com/story/show/54535284
Each activity lists its own pages and links them properly

Bugfix for [#51593657]

https://www.pivotaltracker.com/story/show/51593657