[UI] When file names are too long, user can't see the end of the file name

This is a problem, because folio numbers typically appear at the end of the file name, so files are indistinguishable from each other. For example:

The same problem occurs in the "selected" box top right of the page.

My suggested solution would be to ellipsize (ellipsificate, if you will) the middle of the file name, like my desktop does. So `Einsiedeln__Stiftsbibliothek__Codex_611_010r` becomes `Einsied...611_010r`. Or something. Would that work?

Review issue #130 and the merged pull request #135 for the current state of the fix. The affected UI displays are the file-name listing and the selected box at the top right; done means long names preserve their ending, including the folio number, with a middle ellipsis.

Written by the indexing model from the issue text.