Improvements in timeout handling in Simple.Connect()

Simple.Connect() does a lot of sub-steps, each of them with its own timeout. E.g. Registration has a 60s timeout, and the actual connection attempt has a much much longer timeout, up to 180s. The user should be able to provide a timeout to be applied in the operation, so that ModemManager honors it while it's running its internal steps.

E.g. a user may want to request a full timeout of 120s, and the modem should be allowed to get connected if registration takes 110s and the connection attempt 9s.