2021.8.6

Add AiiDAlab app.

Updates:

• AiiDAlab support.
  This repository can be installed in AIiDAlab as a stand-alone app (#327, @csadorf).
  The requirements have been slightly loosened to support the slower update flow for Python packages.
  Further curation of specifically Materials Cloud databases have been implemented generally.
• Update to latest OPTIMADE Python tools support (v0.16) (#326).

Developer updates:

• Update dependencies (#306, #310, #315, #321, #326):
  • pytest-cov~=2.12
  • pre-commit~=2.13
  • ase~=3.22
  • pylint~=2.9
  • pandas~=1.3
  • invoke~=1.6
  • requests~=2.26
• Update GitHub Actions (#303, #310, #315, #326, #328, #329).