Add KLIFS structure conformation data

[dominiquesydow]

Description

Add structure conformations to opencadd.databases.klifs via KLIFS API Structures.structure_conformations(structure_IDs)
Part of #85

• API: https://dev.klifs.net/swagger_v2/#/Structures/get_structure_conformation
• Model docs: https://dev.klifs.net/swagger_v2/# > ConformationDetails

Todos

Notable points that this PR has either accomplished or will accomplish.

• Add StructureConformations class; add Session.conformations attribute
• Add tests
• Update tutorial with conformations section
• Temporary env fix: Add jsonschema<4.0.0 to env; to be removed once this is fixed: jsonschema 4.0.0 removes compat module Yelp/bravado#478

Questions

None.

Status

• Ready to go

[codecov-commenter]

Codecov Report

Merging #108 (3e58758) into master (9f752aa) will increase coverage by 0.11%.
The diff coverage is 91.66%.