Improve publish releases step

[etpinard]

The current checklist (found here) of:

• wait for CircleCI / Travis / AppVeyor electron-builder and conda builds
• download all the artifacts
• unload them to Github / conda

is a bit of a pain.

Here's my dumb attempt (with notes) from a few months back:

# /bin/bash

# possible ways to automate:
#
# CircleCI:
# - https://circleci.com/docs/api/v1-reference/
# - https://circleci.com/docs/2.0/configuration-reference/#tags
# - https://circleci.com/docs/2.0/workflows/#git-tag-job-execution
#
# Travis:
# - curl https://api.travis-ci.org/repos/plotly/orca/builds to find build number
#   when `d[i].branch === vX.Y.Z`
# - then `wget https://s3.amazonaws.com/image-exporter-travis-artifacts/plotly/orca/$num/$num.1/mac-release.zip`
#
# AppVeyor:
# - curl -H "Authorization: Bearer $APPVEYOR_TOKEN" -H "Content-Type: application/json"  https://ci.appveyor.com/api/projects/AppVeyorDashAdmin/image-exporter
#   to grab `d.build.jobs[0].jobId`
# - then `wget https://ci.appveyor.com/api/buildjobs/$jobId/artifacts/release.zip`
#
# - N.B https://www.appveyor.com/docs/api/projects-builds/#get-project-history
#   does NOT list jobIds !!!
#
#
# Or do this all on CI with:
# https://developer.github.com/v3/repos/releases/#upload-a-release-asset

wget https://1984-99037241-gh.circle-artifacts.com/0/home/circleci/project/artifacts/orca-1.1.0-x86_64.AppImage
wget https://ci.appveyor.com/api/buildjobs/7js6pj38gxt9fcu9/artifacts/release.zip
wget https://s3.amazonaws.com/image-exporter-travis-artifacts/plotly/orca/467/467.1/mac-release.zip

wget https://1982-99037241-gh.circle-artifacts.com/0/home/circleci/project/artifacts/conda-linux-64.zip
wget https://ci.appveyor.com/api/buildjobs/7js6pj38gxt9fcu9/artifacts/conda-win-64.zip
wget https://s3.amazonaws.com/image-exporter-travis-artifacts/plotly/orca/467/467.1/conda-osx-64.zip

cc @antoinerg and #173