Disable some buttons when device is not connected:

• disable Serial -> Manage and Sweep -> Start button when device is not connected
• disable Serial -> Connect button when port was not selected

Pull Request type

Please check the type of change your PR introduces:

• Bugfix
• [] Feature
• [] Code style update (formatting, renaming)
• [] Refactoring (no functional changes, no API changes)
• [] Build-related changes
• [] Documentation content changes
• [] Other (please describe):

What is the current behavior?

There are two issues:

• it's possible to click connect button when no ports selected (e.g. no any physical devices connected)
• it's possible to open serial management OR start sweep when no VNA connected

These crash application.

Issue Number: N/A

What is the new behavior?

Disable connect button when no any physical devices existed.
Disable serial management dialog and sweep start button when no serial was connected.

Does this introduce a breaking change?

• [] Yes
• No

Other information