[WIP] Quality of life improvements and cleanup

[amandasystems]

• Remove unused imports
• Name parameters when supplying
• Fix a few lint warnings
• getProofCertificateAsString now has sensible default arguments
• Replace the deprecated SyncVar with the suggested replacement standard library Java LinkedBlockingQueue of length 1, and fix some race conditions on the way

[amandasystems]

This patch should be possible to graft on to the master branch too, I hope

[pruemmer]

Awesome, thanks! I backported most of the changes to master, and then merged everything into scala-2.13; with the exception of the default arguments, since the proposed values (Format.Auto) would actually cause an exception. Does this fix the exception in Catra?