API: Persistence load change for clients that identify as GUI

With the remote WAN feature there is going to be a slight API change regarding GUI clients and persistence loads. (If your 3rd party client does not set the API.IsGUI variable OR you never send the 'client gui' command this will not affect you). 

Currently:
When a client sends a command to the radio that sets the UDP port, persistence is loaded if the client is the GUI client. All previously persisted panadapters are loaded along with their corresponding slices. If a GUI client does not want persistence to load it must issue the command 'client start_persistence off' *prior* to the 'client udpport <port>' command. 

Planned Changes:
Persistence will now be loaded when the 'client gui' command is issued and *not* when the UDP port is set. This should have no impact on clients *unless* the client depends on not loading persistence. If a GUI client does not want persistence to load it must issue the command 'client start_persistence off' *prior* to the 'client gui' command. 

This change will be compatible with previous versions of radio firmware so updated applications will still work with older versions of SmartSDR. 

Questions? Thoughts?