0.6.0

Changes

• executor as ApiHandle class attribute #95 (jtpio)
• Update RELEASE.md #94 (jtpio)
• Clarify notebook/jupyter_server usage #93 (fcollonval)
• Bump ssri from 8.0.0 to 8.0.1 in /packages/labextension #90 (dependabot[bot])
• Update to JupyterLab 3.0 final packages #87 (jtpio)
• Add instructions to install with conda #83 (jtpio)
• Add Changelog for 0.5.1 #82 (jtpio)