Implement true multi-interface support.

- most of the global handling code in "auto-ng.functions" is separated
into a function "load_interface"
- global code is just parsing parameters
- front-end scripts iterate over parsed interfaces and call sequences of
"load_interface" + their own routine for each interface encountered.

Each interface is handled in a separate sub-shell.
Add default interface list calculation for suspend and resume actions.

Suspend: all running interfaces
Resume: all suspended interfaces
There is no INTERFACES_FILE.
Restore handling of "last" target.

It got pruned somewhy...
Generalise "suspend" default interface calculation for different targets operating on running interfaces.
Fix WPA information status report (--wpa instead of defunct "status wpa").

Old method has been pruned someday and is pretty hard to implement back.