Qt: Fix preference bugs.

Make sure we set the "resolved" member of the column fmt_data struct.

Emitting WiresharkApplication::AppSignals from a modal dialog can cause
event loop problems on OS X. Queue them up in PreferencesDialog and emit
them after closing.

Change-Id: I2de77778a0448db3b87d402e431b8e5f325cbbda
Reviewed-on: https://code.wireshark.org/review/4274
Reviewed-by: Gerald Combs <gerald@wireshark.org>