skip listening `add_token`

[HAOYUatHZ]

• remove built-in tokens in https://github.com/fluidex/dingir-exchange/blob/master/migrations/20210223072038_markets_preset.sql keep it
• deploy several token contracts locally according to markets_preset.sql
• FluiDex.sol should only allow add_token by admin (fluidex/contracts.demo#26)
• admin invokes add_token according to the sequence in markets_preset.sql
• eth_listener skips add_token to exchange, but only watches deposit
  • can make use of cargo feature to disable add_token (fluidex/eth_listener#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.)