Disable keyboard accelerators for the tabs widget

Summary:
Now that there are actions for switching to a specific tab with default
Alt + <number> shortcuts, automatically assigned keyboard accelerators
can result in ambiguous shortcuts when using specific tab names
containing numbers.

Not adding any accelerators for the tabs widget ensures the default
shortcuts work reliably regardless of tab names.

Test Plan:
- Verify there are no ambiguous shortcuts when browsing folders with
names containing only numbers
- Verify other keyboard accelerators still work (menu bar, context menu
and others)

Reviewers: #vdg, #dolphin, ngraham

Reviewed By: #vdg, ngraham

Subscribers: ngraham, kfm-devel

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D24794

src/dolphintabwidget.cpp

@@ -28,6 +28,7 @@
 #include <KRun>
 #include <KShell>
 #include <kio/global.h>
+#include <KAcceleratorManager>
 
 #include <QApplication>
 #include <QDropEvent>
@@ -37,6 +38,8 @@ DolphinTabWidget::DolphinTabWidget(QWidget* parent) :
     m_placesSelectorVisible(true),
     m_lastViewedTab(0)
 {
+    KAcceleratorManager::setNoAccel(this);
+
     connect(this, &DolphinTabWidget::tabCloseRequested,
             this, QOverload<int>::of(&DolphinTabWidget::closeTab));
     connect(this, &DolphinTabWidget::currentChanged,