Provide update commands

[forman]

Expected behavior

Cate shall provide commands to let user update to the latest verion.

• Update Cate CLI via dedicated, simple command, e.g. cate upd [VERSION]
• Update Cate Desktop via dedicated command, e.g. Help menu entry Check for Updates....

Note, update of Cate Desktop must include update to a compatible Cate CLI/WebAPI.

See also #404, which refers to automatic detection of updates for Cate Desktop.

EDIT:

Cate Desktop needs to check Cate CLI service version using cate --version. Currently, this CLI command (as all others) is very slow (takes a few secs), as cate/cli/main.py always seems to import all packages Cate depends on. xarray, dask. gdal and fiona imports are known to be slow. It is therefore a must to at least partly solve #58.

Actual behavior

Cate CLI could be updated using the following command:

$ conda install -c ccitools -c conda-forge cate-cli[=VERSION]

The GUI (Cate Desktop) cannot be updated at all.

Specifications

Cate 1.0

[forman]

Paused this for Cate Desktop, as #477 has higher priority.