Currently, tabbox shortcuts are directly saved to KGlobalAccel when they change, which is inconsistent with the rest of the KCM and leads to confusion regarding Defaults and isSaveNeeded stats.
Let's instead manage the changes internally and just save them to KGlobalAccel on Apply/Save.
m_actionsCollection is only used as a helpful way to store this internal configuration, and doesn't really needs saving to or restoring from config.
BUG: 459325 FIXED-IN: 5.27
Please, test thoroughly. I've might have messed up my own KGlobalAccel shortcuts while debugging this