Summary: This adds a refresh button to the plasmoid if no device is connected.

Test Plan: Refreshing works, and the button only appears when no devices are connected.

Reviewers: #kde_connect, nicolasfella

Reviewed By: #kde_connect, nicolasfella

Subscribers: apol, nicolasfella, #kde_connect

Differential Revision: https://phabricator.kde.org/D11501