Fix ranlib "has no symbols" errors in the codecs directory.

Don't build the G.722 or G.726 codecs for now. Each are wrapped in
"#ifdef HAVE_SPANDSP", which we don't define.

Conditionally compile the SBC codec.

Change-Id: I5f09ff66514f967d4f0611c943b4e6a975b8994b
Reviewed-on: https://code.wireshark.org/review/5690
Reviewed-by: Gerald Combs <gerald@wireshark.org>
Qt: Initial VoIP Calls dialog.

Add Telephony menu items for VoIP Calls and SIP Flows. Put VoIP Calls at
the top, since that seems to be the primary item.

Add configure-time checks for QtMultimediaWidgets in anticipation of
adding a VoIP playback dialog.

Add an icon for the playback button. (Yes, I've been avoiding
GNOME-level gratuitous icons so far but this is one of the rare
occiasions where it makes sense.)

Add a help link define for the VoIP calls dialog.

Change-Id: I5d0799685c598ad9af76fe9667f8ea7d14b66050
Reviewed-on: https://code.wireshark.org/review/5674
Petri-Dish: Gerald Combs <gerald@wireshark.org>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Gerald Combs <gerald@wireshark.org>