Implement the main form of operations view

This is a initial implementation of the form corresponding to the operations view. It provides the controls necessary to insert the properties of a exchange and submit it to the broker set.

![captura de pantalla 2014-07-02 a la s 13 48 50](https://cloud.githubusercontent.com/assets/738507/3455630/d4ec7868-01e4-11e4-8736-c1838ffe932e.png)

This should be `CurrencyAmount(amountTextField.text.getValueSafe.toDecimal, Bitcoin).isPositive` or else invalid values might be passed (like `0.0000000000000001`)