[Applet]Add info messages.

Summary:
Add info messages, when there are no available connections.
"Airplane mode is enabled"
"Wireless and mobile networks are deactivated"
"Wireless is deactivated"
"Mobile network is deactivated"
And "No available connections" with 5 seconds delay.

Test Plan:

Reviewers: Plasma, VDG, jgrulich, ngraham

Reviewed By: VDG, jgrulich, ngraham

Subscribers: ngraham, broulik, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D27392