Konsole tab switching shortcuts

[Nate Graham]

Hello Konsole developers!

https://phabricator.kde.org/R237:d85a57645f94d2d087711d7c608a0c5a46ed7ede 
changes the default KDE keyboard shortcuts for switching tabs 
(KStandardShortcut::tabPrev() and KStandardShortcut::tabNext()) were 
recently changed to be ctrl+pgup/pgdn.

Konsole does not use KStandardShortcut::tabPrev() and 
KStandardShortcut::tabNext(), so it doesn't get that change for free. 
However, using ctrl+pgup/pgdn shouldn't conflict with anything, since 
ctrl+pgup/pgdn don't send signals or anything.

In any event, the prior Konsole tab shortcuts weren't consistent with 
the old standards, either. I've filed a ticket to change the shortcuts 
to be consistent with the new ones: 
https://bugs.kde.org/show_bug.cgi?id=383603

And I've generated a quick and dirty patch on Phabricator to make the 
change: https://phabricator.kde.org/D7354

Nate