Remove unused imports

[fuchsst]

pure code cleanup

• remove unused imports
• replace * imports with explicit package names
• alphabetical reorderd imports
  this MR is based on MR #251

[larsga]

Removing unused imports is great, but the rest amounts to a change in code style. Can we limit this to just the unused imports, please?

[fuchsst]

Removing unused imports is great, but the rest amounts to a change in code style. Can we limit this to just the unused imports, please?

i used intellij's Optimize Imports - removed the implicit changes (e.g. rearangements of the imports) now

maybe some gradle plugin like Checkstyle would make sense to enforce a common code style?
IntelliJ can be configured to refer to the same style-config, so Strg+Alt+L (or Strg-Alt-O) will arrange the code the same.
Or, more general, one can add a pre-commit-hook to apply the checkstyle autofix on changed files.

[larsga]

This PR still has more than just removing unused imports. I don't think this is very important, so perhaps better to skip it rather than put a lot of effort into it? I would have removed the unused imports myself if I thought it was important.