Change EntriesProcessor logic from processing batches of entries to queue

[Tiendil]

Currently, EntriesProcessor starts processing N entries at once in parallel and then waits for all of them to finish before starting the next batch. This could slow down the processing of entries if the processing of one entry gets stuck for some reason.

Instead, we should still process them in parallel but not wait for all of them to finish. As soon as one entry is processed, we should start processing the next one.

It could be achieved by refactoring EntriesProcessor into a queue dispatcher, which controls N background consumers.

caused by gh-170