Reduce line spacing between bibliography entries

[dchiller]

Debra would like less space between bibliography entries on the Source Detail page.

Here's what they look like now on New Cantus:

And for reference, here's the spacing on Old Cantus:

[jacobdgm]

I think this was caused by #1087. Each <li> tag in the bibilography starts on its own line in the text that was entered. Since we're now preserving line breaks with |linebreaks, this causes django to add a <br> beneath each <li> element.

It seems that the formatting of the bibliographies of some sources (and some of their descriptions as well - see #1219) has been done with html tags, and for others, the formatting was done with line breaks. We can accommodate either case (either by including linebreaks or by omitting it), but we can't do both.

[jacobdgm]

noting that this issue is similar to https://github.com/DDMAL/CantusDB/issues/1219, and that we can apply a similar approach (checking for html tags before applying the linebreaks decorator) here as we do there.