tab menu cache does not update when some title is updated

[MichaelVoelkel]

When I change the title of some tab, this title is not directly translated into the cached menu that opens upon clicking on the down arrow.

I could fix this by temporarily offering an "updateSectionContentTabMenus" method to ContainerWidget that just calls on all sections the updateTabsMenu(), but it seems that this is not very clean. Maybe, setting a title should invalidate the corresponding containerWidget's cache. Not sure, if the pointers/references are set in a way that allows for that in an easy way.