Ease Cate installation and updates

[forman]

This is a collection issue for the following issues:

• [x] #367
• [x] #404
• [x] #428
• [x] #439
• [x] #522
• [x] #523

In summary:

• GUI/Desktop users only install Cate Desktop which will auto-update itself and also install/auto-update Cate Core. An installed Cate Core will be auto-detected and can (but not must) be used.
• CLI/Python users just install the Python package cate-cli via conda install -c ccitools -c conda-forge cate-core.

Specifications

Cate 1.0

[forman]

Notes:

• [ ] Before we check if cate-cli requires an update, we must wait to complete any ongoing download/update task by "electron-update".
• [x] must download Miniconda installer into temp dir, we currently use cwd.
• [ ] autoUpdater.checkUpdatesAndNotify() does not notify on Windows 10, seems to be a bug in electron #10864. We need a workaround, so users can reject an auto-update.