Web app: add links to Ethnologue

[MrBrezina]

Ethnologue by SIL has a nice new website with more info on particular languages, for example: https://www.ethnologue.com/language/rme/

[MrBrezina]

With @kontur we agree this is better implemented as a reference in the actual Database and then perhaps used in the web app.

[kontur]

(Essentially, the webapp could show all references, literature reference as such, and web references as links)

[MrBrezina]

Sorry, this has to be separate from sources as those indicate what was used to inform the data. Ethnologue and perhaps references to ISO (e.g. https://iso639-3.sil.org/code/aae) and Language Archives (e.g. http://www.language-archives.org/language/aae) are just an extra feature. Ethnologue has been referred only for a couple of entries, oddly.

[kontur]

Ah, I see; fair enough. Could be a same kind of generic list as sources, though; we can then show both on the webapp, where available. You get to name this baby attribute :P