refs #287 Thread safety, fix "memory access violation"

* some improved comments and information
* QMetaObject::invokeMethod in tool.cpp as thread safe invocation
* common base class for threaded readers
* removed event class, using QMetaObject::invoke instead for forcing calls in main event loop
* stop methods for readers, as used for graceful shutdown (preparing for thread safe destruction of objects)
* graceful shutdown for network context
* calls in tool now via inkoke for thread safety (only thread safe methods called directly)

src/blackcore/context_network.h

@@ -6,6 +6,8 @@
 #ifndef BLACKCORE_CONTEXTNETWORK_H
 #define BLACKCORE_CONTEXTNETWORK_H
 
+//! \file
+
 #include "blackcore/context.h"
 #include "blackmisc/avallclasses.h"
 #include "blackmisc/statusmessage.h"
@@ -22,7 +24,7 @@
 namespace BlackCore
 {
 
-    //! \brief Network context proxy
+    //! Network context proxy
     class IContextNetwork : public CContext
     {
         Q_OBJECT