Updates CL contracts to use event based approach + Drop did:indy2

[Artemkaaas]

The PR contains the following changes:

• Update SchemaRegistry and CrdentialDefinitionRegistry smart contracts to store data in transaction event logs instead of storage
• Endorsement methods for sending schema and credDef
• Update VDR and wrapper methods to match new smart contracts API and resolution flow
• Drop did:indy2 method in favour of using did:ethr
• Updated affected documentation

[Toktar]

Thank you a lot for this big design change!
No requests for change really, just a few questions.
And it will be nice if we can extend tests a bit according to new changes. Not urgent because updated demos cover most cases.