Distinguish Effect Family Id from Effect Family Name...

... and the distinction makes a difference only for built-in effects.

"Id" is meant to persist in pluginregistry.cfg, and is constrained by how
previous versions of Audacity were written.

"Name" is not persistent, so we have the liberty to change it, as done here
for the built-ins.

include/audacity/EffectInterface.h

@@ -64,7 +64,10 @@ public:
    virtual ~EffectIdentInterface() {};
 
    virtual EffectType GetType() = 0;
-   virtual wxString GetFamily() = 0;
+   // Returns a string for internal uses only that may persist in config files:
+   virtual wxString GetFamilyId() = 0;
+   // Returns a user-visible string:
+   virtual wxString GetFamilyName() = 0;
 
    // These should move to the "EffectClientInterface" class once all
    // effects have been converted.