[FEATURE] Send,Exchange: Show Network Fee in confirmation page

Send
![2014-12-25-202439_1366x768_scrot](https://cloud.githubusercontent.com/assets/395821/5553984/15279038-8c74-11e4-9f55-948778199058.png)

Exchange
![2014-12-25-202348_1366x768_scrot](https://cloud.githubusercontent.com/assets/395821/5553988/23908062-8c74-11e4-8155-6296c56a3985.png)

It appears that ```tx._computeFee()``` works too.