Debugger: Make tooltips pinnable.

Replace old debugger tooltip by a new ToolTipManager which
has a list of AbstractDebuggerToolTipWidget with the functionality
to 'acquire' an engine (display its data) and 'release' it
(store engine data and display them as 'previous') and serialization
to XML session data.
DebuggerTreeViewToolTipWidget implements AbstractDebuggerToolTipWidget
for tree model acting as  a filter on watch models.

Rubber-stamped-by: hjk

src/plugins/debugger/debuggerrunner.cpp

@@ -43,6 +43,7 @@
 #include "debuggerstartparameters.h"
 #include "gdb/gdboptionspage.h"
 #include "lldb/lldbenginehost.h"
+#include "debuggertooltipmanager.h"
 
 #ifdef Q_OS_WIN
 #  include "peutils.h"
@@ -344,7 +345,9 @@ DebuggerRunControl::DebuggerRunControl(RunConfiguration *runConfiguration,
             break;
     }
 
-    if (!d->m_engine) {
+    if (d->m_engine) {
+        DebuggerToolTipManager::instance()->registerEngine(d->m_engine);
+    } else {
         // Could not find anything suitable.
         debuggingFinished();
         // Create Message box with possibility to go to settings.