migrate cat features from ixmp.Scenario

[gidden]

update unit test properties file in line with new db-connection args

migrate cat tests to message_ix.Scenario

update clone() API to keep_solution()

update test-db

change all tests to message_ix.Scenario and new API

udpate MESSAGE-version in GAMS code, change to MAJOR.MINOR.PATCH format

remove manual addition of MESSAGE sets and parameters in core.py

harmonize setting of auxiliary set all_modes

stickler appeasement

rename cols for new parameters in tests

add to release notes

Please confirm that this PR has done the following:

• Tests Added
• Documentation Added
• Description in RELEASE_NOTES.md Added

Adding to RELEASE_NOTES.md

Please add a single line in the release notes similar to the following:

- (#XX)[http://link-to-pr.com] Added feature which does something

[gidden]

Per my conversation with @zikolach, we have decided to proceed as follows:

Ok

So just to clarify my understanding

I'm not sure what users may or may not have applied

We know that the schema files had an issue between the two releases

But we now have a system in place to prevent that (notably they live in ixmp source)

So for this release, users may observe migration errors

And given that we have low confidence in whether they will be uniform across the user base

We should probably suggest they simply regenerate their databases