BUG: Entity set status indicator always displays "Saved"

[tillprochaska]

Describe the bug
The status indicator displayed for network diagrams and timelines always displays "Saved", even if a request is currently pending or has failed.

To Reproduce
Steps to reproduce the behavior:

1. Open Aleph in Google Chrome. (The Chrome Developer Tools provide a simple way to simulate that the device is offline).
2. Create a network diagram.
3. Open the Developer Tools and switch to the Network tab. In the Throttling select field, select Offline.
4. Create a new entity in the network diagram.
5. A new node is displayed in the network diagram and according to the status indicator the changes have been saved. However, looking at the network tab in the developer tools, you can see that the requests have actually failed. When you reload the page, the network diagram will be empty.

Expected behavior

• The indicator should correctly reflect when changes are being saved and if requests have failed.
• The indicator should notify users when they are offline. Network issues are the most likely reason why a request would fail, and we should try to prevent problems before they happen.
• When users navigate away from an entity set that has unsaved changes (because it’s currently saving or because there was an error), there should be a prompt asking users to confirm.

We should consider other enhancements when users are offline, for example changing entity sets to be read-only. But in the first place, we should fix what’s already there.

Aleph version
3.13

Screenshots

Additional context
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