Generating a notification doesn't do anything when no geogig layers are present

[BirdSamuel]

Once you click the clock on the notifications tab, select a time, then hit summarize.. nothing happens. On the demo build it shows when data was changed, but any time chosen - nothing shows up.

To reproduce:

• Click clock (Generate Notification) on notifications tab
• Enter any time/date
• Click Summarize

[smesdaghi]

Should perhaps hide the notifications panel when no geogig layers are present and also make the tooltip make clear that the notifications is strictly for geogig layers.