[WIP] API Rework

[derekpierre]

Type of PR:

• [ ] Bugfix
• [ ] Feature
• [ ] Documentation
• [ ] Other

Required reviews:

• [ ] 1
• [ ] 2
• [X] 3

What this does: Based over #547

• Rework of decryption API to use ConditionContext instead of splitting up params for authProvider and customParameters.
• Allow ConditionContext to be populated by developers with authProviders and customParameters before being used for decryption
• Reduce parameters used in calls for decryption -> retrieve flow. Instead only obtain the ritual from the ritual id when the values are actually needed.

Issues fixed/closed:

• Fixes #...

Why it's needed:

Explain how this PR fits in the greater context of the NuCypher Network. E.g., if this PR address a nucypher/productdev issue, let reviewers know!

Notes for reviewers:

What should reviewers focus on? Is there a particular commit/function/section of your PR that requires more attention from reviewers?