[Improvement] - Add option to enable/disable network/serial discovery

Would be nice to have option in preferences to control network and serial port discovery (option to disable it).

In my case (Win7 64bit and 5 network cards) discovery extremely stress CPU. One core usage is up 100% in 3-second intervals. This load is dependent on the number of allowed network interfaces a lot.

Start by reading the preferences handling and tracing where network and serial port discovery is initiated. The issue does not name files or tests; done means users can disable discovery through a preference and the reported CPU load from network discovery is avoided.

Written by the indexing model from the issue text.