Update CI

[rly]

Motivation

Update CI to match the updated CI in HDMF.

1. Move most tests to nightly
2. Add Python 3.9 tests (nightly)
3. Drop Python 3.5 tests
4. Move codecov tests to GitHub Actions
5. Use authenticated docker images (using the HDMF account, which should be fine - if we hit rate limits, we can open an NWB account)
6. Add testing with pre-releases of requirements
7. Add testing with latest upgraded requirements

Checklist

• Have you checked our Contributing document?
• Have you ensured the PR description clearly describes problem and the solution?
• Is your contribution compliant with our coding style? This can be checked running flake8 from the source directory.
• Have you checked to ensure that there aren't other open Pull Requests for the same change?
• Have you included the relevant issue number using #XXX notation where XXX is the issue number?

[codecov]

Codecov Report

Merging #1340 (46fada6) into dev (4ae60bc) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev    #1340   +/-   ##
=======================================
  Coverage   73.89%   73.89%           
=======================================
  Files          37       37           
  Lines        2283     2283           
  Branches      346      346           
=======================================
  Hits         1687     1687           
  Misses        539      539           
  Partials       57       57           

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