fix(*): mousing over tool bar colors annotation in editor

Proposed fix to #1233 (closed) (though maybe behavior desired is slightly different). What this does is:

1. no change to the current behavior when mousing over a citation annotation in the text
2. colored outlines appear when a citation name is moused over in the tool menu

History: 2 disappeared as a side-effect of implementing 1.

A second change was added to this: citations now appear in a standard way, with an outline around the block. This appears around text tagged as a Mixed citation; it also appears this way if it's a paragraph or a list item inside of a Reference List. Internally, Mixed citation is a mark, not a block; but it's set to display as a block now, which should feel a little more intuitive.

The section markers (§) that preceded references have now been taken away – that was always meant to be temporary.