Source daimon priority issue

1. Priority source daimons (priority=1) can be deleted.
2. When recreated, its priority set to 0.

Steps to reproduce:

1. Login as admin, open "Configuration" page, open source with priority daimons. (Check DB table "source_daimons": this source's daimons priority = 1).
2. Uncheck "Vocabulary" and (or) "Result" daimon, save. In DB table "source_daimons": unchecked daimons priority = -1.
3. Open same daimon, create "Vocabulary" and (or) "Result" daimon. In DB table "source_daimons": created daimons priority = 0.

As a result, we have no "Vocabulary" and "Result" daimon with priority = 1, despite the fact that radiobuttons on the "Configuration" page are checked. To restore priority we need to switch "Change source priorities in:" to "Whole application" and change source's "Vocabulary Version" and "Record Counts (RC / DRC)".

Possible solution: do not allow deletion of daimons with priority=1.

Start with the Configuration page flow and the source_daimons table described in the reproduction steps, tracing how disabling and recreating Vocabulary or Result daimons changes priority. Reproduce the sequence as an admin and verify that priority-1 daimons cannot be deleted or that their priority is preserved when recreated.