Implement exponential backoff for commands to load blocks and transfers

[IvanBelyakoff]

Problem

Currently in case of failure commands (transferCommand, findBlocksCommand) retry after predefined interval and in case of limit on max retries they are stopped or in case of infinite retries they just waste the requests.

Implementation

Instead of predefined interval, use exponential backoff. This should help with some errors related to network issues or providers occasionally not available