Add BibTeX citation box (#1325)

[nrllh]

Implemented a citation box in BibTeX format as per the discussion in this issue: #1325

[mgifford]

The linter is pointing to problems in this:

.citation-box pre {
padding: 16px;
border: 1px solid #e0e0e0;
border-radius: 4px;
background-color: #ffffff;
box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
margin-bottom: 20px;
font-family: monospace;
background-color: #f9f9f9;
overflow-x: auto;
white-space: pre-wrap; /* Allow wrapping of long lines */
margin: 0;
}

Both different use of background-color and also margin-bottom & bottom.

Not sure what it should be. I suspect we could just delete:
background-color: #ffffff;
margin-bottom: 20px;

[mgifford]

The linter is pointing to problems in this:

.citation-box pre {
padding: 16px;
border: 1px solid #e0e0e0;
border-radius: 4px;
background-color: #ffffff;
box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
margin-bottom: 20px;
font-family: monospace;
background-color: #f9f9f9;
overflow-x: auto;
white-space: pre-wrap; /* Allow wrapping of long lines */
margin: 0;
}

Both different use of background-color and also margin-bottom & bottom.

Not sure what it should be. I suspect we could just delete:
background-color: #ffffff;
margin-bottom: 20px;