skip listening `add_token`

[0xmountaintop]

• [ ] remove built-in tokens in https://github.com/fluidex/dingir-exchange/blob/master/migrations/20210223072038_markets_preset.sql keep it
• [x] deploy several token contracts locally according to markets_preset.sql
• [x] FluiDex.sol should only allow add_token by admin (https://github.com/fluidex/contracts.demo/issues/26)
• [x] admin invokes add_token according to the sequence in markets_preset.sql
• [x] eth_listener skips add_token to exchange, but only watches deposit
  • can make use of cargo feature to disable add_token (https://github.com/fluidex/eth_listener/issues/3)
• [ ] how can bots&users get tokens
  • minter sends to bots (in another process, not hardcode in contract directly)
    • also need to upgrade bot code? but looks too coupling with ETH-stuff? bots retry until have funds
  • user get USDT from faucet. faucet may need to be configurable?
• [ ] TODO: clean up front-end permissionless listing related stuff (https://github.com/fluidex/tmp_frontend/issues/245)

[lispc]

“deploy several token contracts locally according to markets_preset.sql”：maybe both rollup/exchange/contract read a same tokens.json config file? A single truth rather than several config files (json sql etc.)