refs #391, allow to send aircraft parts from GUI

* GUI component for aircraft parts
* remote aircraft selector component
* Adjusted GUI for internals component
* Enable / disable debug messages from GUI
* Allow to init engines directly
* Removed unused async sort in sequence

In same step fixed found issues in interpolator
* allow to set max rendered aircraft

src/blackmisc/avcallsign.h

@@ -57,6 +57,9 @@ namespace BlackMisc
             //! \sa atcAlikeCallsignSuffixes()
             bool isAtcAlikeCallsign() const;
 
+            //! Observer callsign?
+            bool isObserverCallsign() const;
+
             //! Get callsign.
             const QString &asString() const { return this->m_callsign; }