Add default failbacks

[paltman]

Add fallback messages when no data is returned for a given annotation

[jtauber]

The first thing that's clear is that we're completely inconsistent in the styling of the widget fallback.

• different font size
• different indentation
• "No X available" vs "No Y" vs "No Z found"
• period vs no period

My slight preference is the Named Entities variant. I certainly prefer the smaller font size, less indentation, and no period.

Not sure what which I prefer between "available" or "found" or neither.

[paltman]

I'll make a component called <EmptyMessage> that can have it's own single style.

[paltman]

@jtauber everything is now the same font/size/padding/message. It's a default message in a slot so we can override with specific language. Just let me know what language you want in what widget/place.

[jtauber]

For the side widgets, I'd drop the text-align: center; and change the padding to padding: 0 0 0.4rem;

I understand the centering and margins are needed when in the reader widget (metrical annotation and folios) but in side widgets they take up a bit too much space and draw too much attention.

[paltman]

@jtauber fixed