#17 Feature: instance source(s)

Remove the profile types (stats2 and user) and replace with an instance-source mechanism. So there will only be one profile type which can do both: have a list with instances from `searx-space` and any other sources, including a manual source (for adding urls manual instead of downloading the list). - Instance filters would be per instance-source, or not? - Instance selecting would be per all enabled instance-sources. What if multiple sources share the same instance-url? - Maybe have source priority? So that when there is a duplicate instance-url that it will only show/pick the instance from the instance-source with the highest priority?