Add Midi Prefs and Libraries Prefs help pages

src/prefs/LibraryPrefs.cpp

@@ -239,6 +239,11 @@ bool LibraryPrefs::Apply()
    return true;
 }
 
+wxString LibraryPrefs::HelpPageName()
+{
+   return "Libraries_Preferences";
+}
+
 PrefsPanel *LibraryPrefsFactory::Create(wxWindow *parent)
 {
    wxASSERT(parent); // to justify safenew

src/prefs/LibraryPrefs.h

@@ -28,6 +28,7 @@ class LibraryPrefs final : public PrefsPanel
    LibraryPrefs(wxWindow * parent);
    ~LibraryPrefs();
    bool Apply() override;
+   wxString HelpPageName() override;
 
  private:
    void Populate();

src/prefs/MidiIOPrefs.cpp

@@ -286,6 +286,11 @@ bool MidiIOPrefs::Validate()
    return true;
 }
 
+wxString MidiIOPrefs::HelpPageName()
+{
+   return "MIDI_Devices_Preferences";
+}
+
 PrefsPanel *MidiIOPrefsFactory::Create(wxWindow *parent)
 {
    wxASSERT(parent); // to justify safenew

src/prefs/MidiIOPrefs.h

@@ -33,6 +33,7 @@ class MidiIOPrefs final : public PrefsPanel
    virtual ~MidiIOPrefs();
    bool Apply() override;
    bool Validate() override;
+   wxString HelpPageName() override;
 
  private:
    void Populate();