feat(vaults): add assets and token fields to endpoint

[nymmrx]

Discussed in discord PMs.

Short summary:

• fetch assets from https://github.com/iearn-finance/yearn-assets and fallback to https://github.com/trustwallet/assets
• fetch token info from vault's token.address
• add a displayName for vaults and tokens
• /vaults/all now follows the format:

  [
  {
      "address": "0x29E240CFD7946BA20895a7a02eDb25C210f9f324",
      "type": "v1",
      "name": "yearn Aave Interest bearing LINK",
      "symbol": "yaLINK",
      "decimals": "18",
      "token": {
          "address": "0xA64BD6C70Cb9051F6A9ba1F163Fdc07E0DfB5F84",
          "name": "Aave Interest bearing LINK",
          "symbol": "aLINK",
          "decimals": "18",
          "displayName": "aLINK",
          "icon": "https://raw.githubusercontent.com/iearn-finance/yearn-assets/master/icons/tokens/0xA64BD6C70Cb9051F6A9ba1F163Fdc07E0DfB5F84/logo-128.png"
      },
      "inceptionBlock": "10599617",
      "apy": {
          "inceptionSample": 11.680565331008788,
          "oneMonthSample": 0.5690614438140246
      },
      "displayName": "aLINK yVault",
      "icon": "https://raw.githubusercontent.com/iearn-finance/yearn-assets/master/icons/tokens/0x29E240CFD7946BA20895a7a02eDb25C210f9f324/logo-128.png"
  },
  {"..."}
  ]