printers: Fix few smaller issues

This merge request fixes 3 small issues in current Printers panel:

1. blurred icons of printers in the list

   • this has been fixed by aligning the icon to center without asking to fill the area, the icon is not blurred then

2. asymmetric placement of search entry in the new printer dialog

   • allowing the entry to expand horizontally fixes this

3. title of details dialog is not bold

   • it should be bold since beginning since all the other dialogs have bold titles (I mean bold font, not a text with strong opinions :) )

Issue #1587 (closed)