Large changes to Socket/UPS, DATA-STALE error handling

[gbakeman]

• New Nut_Exception constructor to allow specifying NUTResponse instead of _Exception_Value
• Shifted some responsibility of error handling out of Socket class and into UPS class. These are some major changes and need testing.
• Merged Create_Socket code into Connect code
• Renamed and then commented-out IsKnownUPS function. Feels like this should be a part of the UPS class, but regardless, we'll know if there's an invalid UPS the moment a command is run for one.
• Simplified & renamed Query_Desc function
• Added a few events to the UPS class for informing any listeners of issues
• UPS no longer handles socket errors, and instead passively notifies listeners about one
• GetUPSVar supports DATA-STALE errors and will retry 3 times to get the data, and then take the default value and raise an event about the error.
• If error is encountered when opening the ListVarGUI, display a message box and close the form.
• Removed the Unknown_UPS event and modified the GUI to handle future errors.

Resolves #21