Exclude-prefixes not updated correctly

[Mixaster995]

Expected Behavior

Excluded-prefixes should exactly match prefixes from source file.

Current Behavior

Excluded-prefixes only appended never removed

Scenario

1. Initial request starts
2. Excluded prefixes server reads prefixes from file and appending it to request's excluded prefixes
3. After initial request refresh mechanism uses the same request object(with already added excluded prefixes)
4. Excluded prefixes server reads prefixes from file(which might be modified at this moment) and if it's different set of prefixes than on initial request just appends it to request.
5. Every refresh it repeats, so if file with excluded prefixes changes often, it'll just grow excluded prefixes

Possible solution

Add client chain element, and on request it's going to save excluded prefixes added to request by client, and on request response change possibly modified request prefixes back to saved ones.
Also, update client's cmd-s to use this chain element

[Mixaster995]

@edwarnicke could you, please, take a look to see if you okay with suggested solution
It prepared it in #1180