add --noextensionsinterface (-nEI) + checks if interface exists

[calculatortamer]

allow user to use extensions without specifying an interface instead of erroring out, so they can use extensions that dont require an interface like --handshake-capture
also add checks in extensions.py so the manager dont crash if an extension tries to do something with the None interface

(add --noextensionsinterface (-nEI) + checks if monitor interface exists in pywifiphisher.py and extensions.py)