Fix toolbar button text hiding opt
REVIEW: https://phabricator.kde.org/D8151
There is a bug with toolbar button's text. If you open toolbar's context menu you'll be able to hide button caption for each button separately. You can disable all of them which is very convinient if you enabled a lot of plugins that add new buttons to toolbar.
But when KTorrent is relaunched it forgets this setting for very first subpanel (by default it contains 2 buttons: torrents & plugins). All other buttons keep their text hidden.
This fix allows KT to save and load these buttons state properly.