Restore Mojang skins proxy implementation

[erickskrauch]

This is the implementation of #1. For now, I have the next unimplemented or unresolved tasks:

• Results are not cached
• Adding of the same username multiple times to the queue is not prevented
• Have no solution for the case, when username submitted while its already taken in queue iteration
• No tests
• Always return nil when submitted username doesn't satisfy Mojang username requirements (3-16 characters, no spaces, A-Z, 0-9, _)
• Split processing to 2 steps: exchanging usernames to uuids and obtaining textures for uuid and let manually call the second step
• Split storage to storage to map username -> uuid and uuid -> textures
• Implement TexturesStorage interface as in-memory storage, that will clean its values older than 1 minute
• Any network error while querying Mojang's API will cause panic
• Implement UuidsStorage in Redis. It should store data for 30 days
• No logging mechanic
• Obtaining textures after usernames to uuids exchange should not await all operations finish
• Queue not integrated with the application
• Update tests for HTTP layer of the application
• Test behavior of exists authlibs that already used on clients when /textures request returns empty 204 response
• Handle possible panic from Mojang's queue, log it and recover
• Run load testing in profile mode. Try to fix the bottlenecks if any
• Update README.md file (note on the processing queue and signedTextures request proxy param)
• Add CHANGELOG.md file

[erickskrauch]

• Multiple requests for signed textures with proxying results in the chrly property being duplicated..