Feature/#26 implement groups entity

[LaimeJesus]

closes #26

There is a GroupCurrencyTokenFactory contract deployed at: 0x7dAF5fE2B112A90cCf8b6FE8bbDFB5de1AbAE8c8 in the xDai network

Description

This PR adds the following changes:

• adds the GroupCurrencyToken entity:
  • symbol
  • name
  • owner
  • hub
  • treasury
  • mintFeePerThousand
  • creator
  • suspended
  • onlyOwnerCanMint
  • onlyTrustedCanMint
• adds GroupCurrencyToken and GroupCurrencyTokenFactory abis
• adds GroupCurrencyTokenFactory as dataSource in subgraph.yml
• adds group creation handler file to map the creation events from the factory

How to test

• copy .env-xdai.example -> .env
• need to modify: ACCESS_TOKEN, SUBGRAPH_NAME, SUBGRAPH_NETWORK, START_BLOCK variables
• deploy subgraph: npm run deploy hosted-service-deploy
• check deployed service

Example

Check deployed Subgraph in Hosted Service:

• https://thegraph.com/hosted-service/subgraph/laimejesus/circles-local