Connect "all volumes" page to Wagtail and Django backend

[blms]

In this PR

• Integrate data from Wagtail and Django into the new design for the volumes list
  • Simplify the code for handling the returned list of volumes
  • Create a form for handling sort, order, and display (grid vs list)
  • Create a new form widget called CustomDropdownSelect that uses the uk-navbar-dropdown ui components
• Completely remove the unused all volumes view/template from Django

Questions

• Do we want author and date added to appear on the grid item for each volume? They're available but commented out since they weren't present in the redesigned page.
• Is the list view designed?
• It looks like list view vs grid view is something controlled by the Wagtail content admin/editor, not the end user, in the current configuration. Given that is the case, should we remove this piece from the frontend?

(note that this is reusing a decent amount of #1054, but with Wagtail and not Django view)

[jcmundy]

I would think that yes we want the author and date added. The title also needs an ellipsis after a certain number of characters (not important for Sounding Spirit, but Readux.io has some long titles.

If we leave out the list view, the option needs to be removed here:

readux/apps/cms/models.py

Line 60 in 473046d

("List", "List"),

We could also as easily leave in the option with the current styling from

readux/apps/templates/cms/volumes_page.html

Line 103 in 473046d

{% if page.layout == 'List' %}

[blms]

@jcmundy Thanks for the feedback!

To clarify on the last point, my poor wording was intending to ask whether or not this should be removed from Yang's design:

Since it would appear to control something that's currently only controllable from the Wagtail admin, not by a front end user.

That said, we can decide if the list view should exist at all, and if so, whether it should be controlled by admins in Wagtail or by users clicking that menu item.

[jcmundy]

Ahhh - yes, that should be removed from the frontend design. :)