Refresh button is sensitive even if offline #396
Description
Problem
The refresh button is sensitive even if you're disconnected from network, and clicking it behaves as if it's really checking for updates, which looks strange.
Proposal
Make the refresh button insensitive when disconnected from network or/and suggest users to connect to network to check for updates.
Prior Art (Optional)
AppCenter shows a banner for this:
Check for Updates menuitem is sensitive though:
