Index order events

[mariacarmina]

Fixes #125 .

Changes proposed in this PR:

• index OrderStarted
• index OrderReused
• tests
• create orderSchema
• store orders in the db

[mariacarmina]

needs integration tests + price

[mariacarmina]

CURRENT PROBLEM:

getERC721Address smart contract function retruns a different NFT address -> returns a different DID checksum which cannot be identified in the DB.
For metadata events, event.address (which is == NFT address) is a different address (rather than getERC721Address) and stores the DDO with a certain checksum which does not correspond with the one generated in OrderStarted processor.

[mariacarmina]

Here is the source code from the contracts which sets the erc721Address https://github.com/oceanprotocol/contracts/blob/main/contracts/templates/ERC20Template.sol#L268.

[bogdanfazakas]

we can still merge the PR as it is since it is working, without the more detailed things like the order schema or how we work with the db

[mariacarmina]

without the more detailed things like the order schema or how we work with the db

From what I've discussed with @alexcos20, the preferred schema was something that follows this model:

{
 id:   txID,
 type: 'startOrder' | 'reuseOrder'
 timestamp: block.timestamp,
 consumer,
 payer,
 startOrderId: (if type reuse)
}

@alexcos20 can you confirm as well and review it?