Agent: add initial background script

[sohkai]

Not yet tested, and has a few todos to complete (pending more work on aragon.js).

Passes to the frontend data in the form of:

{
  balances: [
    // This is the same as Finance's; all numerical values are strings meant
    // to be converted into normal numbers or BN.js objects on the frontend
    {
      address,
      amount,
      decimals,
      name,
      symbol,
      verified
    }
  ],
  transactions: [
    {
      id,  // <transactionHash>.<transactionIndex>.<logIndex>; not meant to be shown to humans
      date,  // Similar to Finance's; in milliseconds as a normal number
      description,  // string
      safe,  // boolean; only true if `SafeExecute()` was used (for later use)
      tokenTransfers: [
        {
          amount,  // string; BN number
          from,  // address of sender if transfer was to the Agent app, null if not
          to,  // address of the recipient if transfer was from the Agent app, null if not 
          token,  // token address
        }
      ],
      transactionHash, // string bytes64 hash for the transaction
      type, // string; see transaction-types.js (one of 'direct deposit', 'direct transfer', or 'contract interaction')
    }
  ],
}

The null possibility for the from and to fields of the tokenTransfers is intended to help front-end filtering based on incoming / outgoing transactions, but can be changed to suit the frontend as necessary.

Note that tokenTransfers is an array that can hold multiple token transactions (a single transaction that executes a contract can include many internal token transfers). For flexibility / simplicity, it currently does not do any grouping on the transfers, although we may want to do so in the frontend (sum all amounts for the same token) to meet the current designs.

There are a few edge cases in the current reducing that will require more complex detection to provide good UX. One example is a single transaction invoking multiple Agent executions that each transfer tokens. Another is directly receiving ETH onto the Agent's proxy from a contract interaction, as it's difficult to correlate receiving ETH with a contract execution based solely on the events in the general case. In the current state, these cases will be presented slightly confusingly to users (most likely symptom is duplicate / multiple transaction entries for a single data).

---

TODO:

• Test, especially decoding token transfers and receiving ETH through contract interactions
• Upgrade aragon.js to automatically include AppProxy events ABI (ProxyDeposit is not currently automatically decoded)
• Upgrade aragon.js with API to fetch current app's contract address
• Upgrade aragon.js with API for describing radspec
• Add description fallback with check to function signature registry

[AquiGorka]

Transactions has a tokenTransfers array which means each transaction can have multiple token transfers, the designs expect one amount (colored to refer to deposit/withdrawal):

What would be the best approach here?

Update: designs expect a token too, which token should be displayed here?

Update 2: same with Source/Recipient it expects one address

[sohkai]

The best option might be to use the DataView's "entry expansion" to show multiple transactions.

If we don't want to do that now though, we could just say "multiple tokens" and "multiple" for source / recipient for the row.

[AquiGorka]

How about this:

• If there is only 1 tx use that data
• If there's more use the word multiple as you suggested

[coveralls]

Coverage remained the same at 97.914% when pulling b988b3b on newstyle/agent-data into e5fa726 on newstyle/agent.

[sohkai]

Suggested change

	.call('initialized')
	.call('hasInitialized')

[sohkai]

Suggested change

	'Could not start background script execution due to the contract not being connected to a network:'
	'Could not start background script execution due to the contract not being connected to a network'

[sohkai]

Closing for #1082