Don't reset existing channel labels when adding new channels

[vedranMv]

Is your feature request related to a problem? Please describe.
On the first session, where there's no serial labels in config file, adding new channel will clear labels for existing channels. If config exists, they will be pulled from the config.

Describe the solution you'd like
Channel label never gets reset unless user has manually cleared it

Describe alternatives you've considered
Potential workaround is to either exit the app, or connect/disconnect the input before adding new channels.