Error on migration about chestshop-3

[Phoenix616]

That commits adds a prettier error printing and an info every 60 seconds while the slow migration is running. Unfortunately doing it async isn't that easy to implement as the plugin heavily relies on the accounts data to properly work but I keep that in mind, maybe I find a good solution.

[Phoenix616]

These errors are to expected if you have a lot of players while converting to the new format as the previous implementation did not check whether or not the short sign name was unique (which the new one does). I might make the error less noisy to avoid confusion in the future.

Adding a progress to the slow migration is a good idea, I'll look into that. (The normal migration in case of no short name conflicts should be a lot faster anyways)

[rautamiekka]

^ I imagine a status report every X seconds (assuming the process haven't finished sooner) would be the best, and maybe easiest to code.

Report every X records is a possibility.