Single cursor position in addCitation dialog

[fbennett]

Navigation in the addCitation dialog might be more intuitive if the cursor appeared only in the panel that is active for editing, with only the "add" or "remove" button enabled for the currently highlighted source. The attached patch implements that behavior. It seems nice to me, see what you think.

While setting this up, I was getting segfaults in the browser when attempting to remove the selection in the tree while focus was in the selections panel, due to a catch-22 firing of the select action on the tree node. I was able to avoid that by using "onfocus" events to control the highlights.

[fbennett]

addCitation_focus.patch (revised)

[fbennett]

After thinking over the changes, I realized that using "onfocus" to avoid selection events added an unnecessary layer of complexity. I've revised the patch to use the suppression toggle that was already in there for events on the tree (and a fresh one that I added for events on the selected items list). This keeps things consistent with the existing code, and doesn't touch addCitationDialog.xul.

[simon]

(In [6129]) closes #1665, Single cursor position in addCitation dialog (thanks Frank!)