Edit metadata dialog: Add special author edit

Edit metadata dialog: Facilitate editing the authors for books that have
a large number of authors, by using a dedicated "Edit authors" tool, which
you can launch by right clicking the authors in the edit metadata dialog
and selecting "Edit authors". Fixes #1255288 [[Enhancement] Display authors in editable popup window](https://bugs.launchpad.net/calibre/+bug/1255288)
Expand shorthand properties in filter CSS

Conversion: Fix specifying shorthand properties in filter css not
working. Now all shorthand properties automatically filter out all the
properties they are shorthand for.