Upgrade syntax to Python 3.7

[nsoranzo]

using ack --type=python -f | grep -v '^tools/' | xargs pyupgrade --py37-plus

Also more refactoring of Python files in packages/ .

How to test the changes?

(Select all options that apply)

• I've included appropriate automated tests.
• This is a refactoring of components with existing test coverage.
• Instructions for manual testing are as follows:
  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]

License

• I agree to license these contributions under Galaxy's current license.
• I agree to allow the Galaxy committers to license these and all my past contributions to the core galaxy codebase under the MIT license. If this condition is an issue, uncheck and just let us know why with an e-mail to galaxy-committers@lists.galaxyproject.org.

[bgruening]

Cool, but I guess we should wait until @jmchilton work has landed?

[nsoranzo]

Which one? This is very small compared to the black PR.

[jmchilton]

I have reservations about this but my open PRs are a non-issue here, feel free to merge.

[nsoranzo]

Rebased, and I've converted (almost) all format strings to f-strings. Ready for a re-review.

[nsoranzo]

Thanks for the reviews @bgruening @ic4f !