Refactor/minimize store usage

[satello]

Changes to use the chain for most timestamps and dispute data.

Note: this is largely untested. Do not use in production. Pushing to stabilize broken develop.kleros.tech environment for development.

[coveralls]

Pull Request Test Coverage Report for Build 671

• 55 of 90 (61.11%) changed or added relevant lines in 8 files are covered.
• 11 unchanged lines in 4 files lost coverage.
• Overall coverage increased (+5.8%) to 48.968%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/contracts/abstractions/Arbitrable.js	0	1	0.0%
src/resources/Notifications.js	0	4	0.0%
src/utils/StoreProviderWrapper.js	0	13	0.0%
src/contracts/implementations/arbitrator/KlerosPOC.js	36	53	67.92%

Files with Coverage Reduction	New Missed Lines	%
src/resources/Notifications.js	1	27.27%
src/resources/Disputes.js	2	65.0%
src/utils/StoreProviderWrapper.js	2	1.6%
src/resources/Auth.js	6	9.52%

Totals
Change from base Build 666:	5.8%
Covered Lines:	482
Relevant Lines:	868

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💛 - Coveralls