FreeBSD wifimgr

All the following changes have been integrated in wifimgr-1.12, except Schift-click1 feature replaced by new behavior of "Any BSSID" (folding of all same-SSID networks into one line).

See https://opal.com/src/wifimgr/ for official and latest versions.

Add some features to wifimgr-1.11:

• Shift-click-1 on a network checkbox select/unselect all networks with the same SSID;
• new button "Hide unavailable"/"Show all" button to display only available networks or available+recorded networks (by default displays available+recorded networks);
• can now order networks by SSID (default), signal strength or channel;
• wifimgr automatically loads/saves user choices in ~/.wifimgr;
• correct some clang warnings.