Fix selectors for file list elements

When the checkbox was moved to where the favourite icon was shown before
the layout of the file list was modified. The first column is no longer
the file name, so neither the thumbnail nor the name link were found.
Due to this the thumbnail was not set to the appropriate icon, and the
dummy event handler was not removed from the name link, so clicks on the
name were basically ignored. Now the selectors are based on the
".filename" CSS class instead of relying on the column position.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>