Extract method and event ABIs from existing contracts dataset

[rimrakhimov]

We have an existing dataset of ABIs available from the verified contracts. We have no active usage of that right now, but we can use it in many ways as part of our sig-provider service. We need to explore such an integration more.

• Update ABIs of the existing contracts as there was a bug in verifier service which caused non-full ABIs to be returned (see verifier: fix non-full abi into responses #504)
• Extract existing ABIs from the database

[rimrakhimov]

• Events - Verification: method to decode undecoded event logs #684