Remove paster cli

[davidread]

Fixes #5110

Proposed fixes:

• CLI commands which used paster are deleted (they were recently replaced with the 'ckan' commands, using click, compatible with python 2 and 3)
• CkanCommand and other helpers in ckan/lib/cli.py are marked as deprecated, to alert extensions that use it. Also noted in the changelog.
• CLI tests (test_jobs.py and test_user.py) have been converted from testing paster CLI to the new CLI. It looks like @smotornyuk did a similar job 9c1e2877780bd3b6f56 independently around the same time. Some of @EvgeniiaVak's work in this PR are improvements on @smotornyuk 's work. Other sections merely express the same thing slightly differently, but it was easier to leave these bits in - I don't think that makes any difference.

This is mostly @EvgeniiaVak's work (from #5129). I simply marked the deprecations and deleted the superfluous test_cli.py.

Extension paster commands still work (python2):

$ paster --plugin=ckanext-harvest harvester sources
2020-03-02 03:45:22,574 INFO  [ckan.cli] Using configuration file /etc/ckan/default/ckan.ini
2020-03-02 03:45:22,580 INFO  [ckan.config.environment] Loading static files from public
2020-03-02 03:45:22,643 INFO  [ckan.config.environment] Loading templates from /vagrant/src/ckan/ckan/templates
2020-03-02 03:45:26,000 INFO  [ckan.config.environment] Loading templates from /vagrant/src/ckan/ckan/templates
2020-03-02 03:45:26,022 DEBUG [ckanext.harvest.model] Harvest tables defined in memory
2020-03-02 03:45:26,035 DEBUG [ckanext.harvest.model] Harvest tables already exist
2020-03-02 03:45:30,410 INFO  [ckan.config.environment] Loading static files from public
2020-03-02 03:45:30,460 INFO  [ckan.config.environment] Loading templates from /vagrant/src/ckan/ckan/templates
2020-03-02 03:45:31,495 INFO  [ckan.config.environment] Loading templates from /vagrant/src/ckan/ckan/templates
2020-03-02 03:45:31,511 DEBUG [ckanext.harvest.model] Harvest tables already exist
2020-03-02 03:45:31,956 CRITI [ckan.lib.uploader] Please specify a ckan.storage_path in your config
                         for your uploads

There are 0 active harvest sources

Features:

• includes tests covering changes
• includes updated documentation
• includes user-visible changes
• includes API changes
• includes bugfix for possible backport

Please [X] all the boxes above that apply

[amercader]

@smotornyuk this looks good to me. If you are happy with the tests we can merge

@EvgeniiaVak thanks for your work on this!

[amercader]

So meta :)

[smotornyuk]

Yes, I've finally some time fo review. Looks nice - I'm merging it

[davidread]

Thanks @smotornyuk