Make `WalletActor` write current transactions to wallet properties

So they can be read by the API and therefore the UI.
Introduce transaction properties in UI

This change moves the UI wallet properties into its own class
`WalletProperties`. The property binding functionality is also moved to
the trait `PropertyBindings`. Then, new classes are added to model the
transactions properties for the UI.
Implement the transactions table view in `WalletView`

So it shows a prelimiary view of the transactions.
Merge pull request #249 from sortega/issue/39_serial_exchanges

Steps towards partial matching
Remove meaningless property `amount` from `TransactionProperties`

And fix some style issues.
Make Exchange.Progress track two bitcoin amounts

The bitcoin exchanged is not the same for the buyer than for the seller
as the latter bears the bitcoin fees.
Remove fiat amounts from progress description
Replace transactions by wallet activity in `WalletProperties`

Instead of recording the wallet transactions in the Coinffeine properties, it's
much more useful to record its activity. That allows the UI to know the amount
that was reverted to/from the app wallet.
Merge pull request #250 from apoloval/task/list-tx

Show the wallet transactions in Wallet View
Add a proportional allocation algorithm
Currency amount convertible to indivisible units
Add Price.scaleBy
Add more overloads for Bitcoin.fromSatoshi
Fix amount calculator computations
Introduce RequiredFunds

And make it the type of choice when AmountsCalculator tells you how
much funds block for an order.
Merge pull request #251 from sortega/issue/39_serial_exchanges

Fix how exchange amounts are computed