No prompt to save changes to modified IRC servers in "Network" activity

Test case

Steps

1. Connect to core
2. Go to overflow menu → Core Settings → edit an existing network
3. Add a new IRC server
   • Specify anything for the host
4. Save the new IRC server
5. Press "Up" or the "Back" button on the Network activity without pressing Save

Expected

Quasseldroid prompts about discarding changes.

Actual

New/changed highlight rules are lost without warning.

Additional

Ignore List properly handles this. Similar to the issue for Highlights.

Marking as Priority: Normal as this is a data loss bug, but for an infrequently changed section.