Merge pull request #276 from sortega/towards_currency

Improvements on the `currency` package
Fix CrossedOrdersTest assertions
Merge pull request #277 from sortega/fix_it

Fix CrossedOrdersTest assertions
Remove compilation warning on ServiceActor

Remove pattern match cast that was anyway ignored due to the type 
erasure improve how it will fail in runtime if an Start() with invalid
is received.
Merge pull request #278 from sortega/issue/51_warning

Remove compilation warning on ServiceActor
Add some convenience functions to ScalaFx pimps
Add a new `OrdersTable` control based on a tree table

Replace the regular orders table by a operations tree table. This requires some
changes in the properties in order to have an abstract bean to represent both
orders and exchanges.
Override `toString` in exchange data artifacts

This makes possible to use them to compose human readable texts based on
exchange state.
Add price column to operations table

And improve `Price#toString` to provide a normalised price.
Upgrade to ScalaFX version 8.0.20
Add exchanges to operations view

Introduce `ExchangeProperties` and adapt `OperationsTable` to display exchange
information.
Change default window dimensions

From 600x400 to 1024x600.
Merge pull request #280 from apoloval/fix/window-size

Change default window dimensions
Merge pull request #279 from apoloval/task/cf-72

Display order exchanges in UI
Replace `DecimalNumberTextField` in `OrderSubmissionForm`

By more convenient control `CurrencyTextField`.
Remove unused and deprecated class `DecimalNumberTextField`
Merge pull request #281 from apoloval/fix/currency-textbox

Replace `DecimalNumberTextField` in `OrderSubmissionForm`