[Kicker/Kickoff] Re-word "Manage <app>..." menu item for greater clarity
Even with the Discover icon added in D23623, the text is still fairly unclear,
especially for the common case of wanting to uninstall the app.
This patch re-words the menu item to add that all-important word "Uninstall", while not
losing any of the current meaning.
Reviewed By: nicolasfella
Differential Revision: https://phabricator.kde.org/D23652