Cleaning up some error messages
Merge pull request #424 from LocutusOfBorg/414-fix

Cleaning up some error messages 1/2
Fixing issue #189 from Simon Sokolov
Aligned with pull request #390, for better performances
Merge pull request #418 from LocutusOfBorg/189-fix2

Fixing issue #189 from Simon Sokolov
This takes care of regaining root privs before attempting to remove iptables rules and restoring ip forwarding
fixes issue #414
Merge pull request #426 from LocutusOfBorg/414-fix2

414 fix2 2/2
delaying progress dialog based on time
introduce a new function for plugins to self-destruct
threading for search_promisc plugin
threading for scan_poisoner plugin
threading for link_type plugin
automatically refresh plugin list (Gtk)
automatically refresh plugin list (Curses)
Update Gisle Vanem mail address
Fixed wrong link with embedded curl and sslstrip plugin
Fixed privileges problem, you cannot setup redirect if you are not root
Fixed polkit install failure on macOSX
rename plugin_kill to plugin_kill_thread
Merge pull request #427 from koeppea/gtk-progress-delay

delay gtk progress dialog based on time