Elliptic Curve landing page

[jenpaulhus]

This PR adds a landing page for elliptic curves (similar to the landing page for modular forms) and finishes fixing issue #2479

http://localhost:37777/EllipticCurves/

It could use some feedback before it is merged.

For EC/Q things work pretty smoothly. The "Elliptic curves" bread goes to the page above (click on "Elliptic curves" in the bread on any EC page).

For ECNF, this does change the behavior of the bread a bit. It adds a Q(\alpha) bread at the top of the main page and the RCS (RSC? CRS?) knowls:
http://localhost:37777/EllipticCurve/

But then for individual pages, it does not currently add a Q(\alpha) bread as there is already a Q(blah) bread added for that particular \alpha. I could add Q(\alpha) also, but I wasn't sure if that made the bread too long.

I can easily change this behavior, just wanted to get feedback before doing so.

Also, I have commented out some lines of code that I will remove once this is ready to be merged, but I wanted to keep them in to easily undo parts as needed (adding this note as much to remind myself later as for anyone else).

[JohnCremona]

Thanks for doing this @jenpaulhus ! I think we need more eyes on this than mine. Initial thoughts are positive, but also:

• on the new page you could write in full "Elliptic curves over number fields Q(alpha)". The short version in the sidebar was for space-saving reasons only with a hope that users would guess what sort of fields Q(alpha) referred to but there is no space issue here
• at the same time, until we finish implementing the feature that searches for curves over number fields will include curves over Q in their results, perhaps "other than Q" needs inserting at the end of the second item.
• apart from breadcrumbs, shouldn't we have an entry "Elliptic curves" in the sidebar bringing users to this new page? Probably as well as the separate sidebar items going directly to curves over Q and over number fields (or everyone would get frustrated by having to click twice where now they only need to click once).
• I suppose that we could then extend this to have a Curves page listing elliptic, genus 2, etc, and one day also even a Varieties page, but that can be done later if at all.