folderspanel context-menu option "Limit to Home Directory" should be always visible

Summary:
Only by chance I discovered that this option is visible but only when inside home. Before that I always edited dolphinrc to reenable it.
I think it's less confusing to always show it but toggle its enabled state

Test Plan:
compile and run
show folderspanel context-menu in different places

Reviewers: Dolphin, emmanuelp, ngraham

Reviewed By: Dolphin, ngraham

Subscribers: elvisangelaccio

Tags: Dolphin, KDE Applications

Differential Revision: https://phabricator.kde.org/D9662