Changed QML Inspector from a separate global mode to a plugin.

The new QML Inspector depends on DebuggerPlugin. Also added a dropdown menu into
the debugger toolbar from which the user can select the used debugging
language, e.g. C++ or QML.

src/plugins/debugger/debuggerconstants.h

@@ -38,7 +38,7 @@ namespace Constants {
 // modes and their priorities
 const char * const MODE_DEBUG           = "Debugger.Mode.Debug";
 const int          P_MODE_DEBUG         = 85;
-
+const char * const LANG_CPP             = "C++";
 // common actions
 const char * const INTERRUPT            = "Debugger.Interrupt";
 const char * const RESET                = "Debugger.Reset";