Qt: Re-enable menu icons.

The GNOME HIG says "Where a corresponding toolbar icon exists, a menu
icon should mirror its design." The Windows and OS X HIGs say that you
should use them for common or familiar actions but otherwise avoid
clutter. I think icons in the "File" menu look like crap. Try to strike
a balance.

Use the 16x16 application icon for both the main web site and the wiki
since that's the favicon used on both sites.

Assume that "Reload" isn't used very often and remove it from the
toolbar.

Don't use a menu icon for the about box.

Other minor fixups.

Change-Id: I855211c218d266c2e9ed5acbe05a08750ab6d157
Reviewed-on: https://code.wireshark.org/review/4246
Petri-Dish: Gerald Combs <gerald@wireshark.org>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Gerald Combs <gerald@wireshark.org>