feat: add user preferences service

[leafty]

Fixes #64.

Note: merging into a feature branch.

[coveralls]

Pull Request Test Coverage Report for Build 6720551860

• 155 of 214 (72.43%) changed or added relevant lines in 14 files are covered.
• 3 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-1.2%) to 86.183%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
bases/renku_data_services/data_api/main.py	1	2	50.0%
components/renku_data_services/user_preferences/models.py	12	13	92.31%
components/renku_data_services/user_preferences_migrations/versions/b1616cce1545_add_user_preferences.py	11	12	91.67%
components/renku_data_services/user_preferences/orm.py	21	23	91.3%
components/renku_data_services/user_preferences/blueprints.py	28	35	80.0%
components/renku_data_services/user_preferences/db.py	23	70	32.86%

Files with Coverage Reduction	New Missed Lines	%
bases/renku_data_services/data_api/main.py	1	62.22%
components/renku_data_services/crc/db.py	2	85.9%

Totals
Change from base Build 6718704699:	-1.2%
Covered Lines:	2626
Relevant Lines:	3047

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💛 - Coveralls

[olevski]

Is this ready for review @leafty?

[leafty]

Is this ready for review @leafty?

Yes it is 😄