Merge pull request #132 from sortega/task/165_exchange

Replace *Exchange hierarchy by a Exchange case class
Introduce EventChannelProbe

It makes easier to assert on Coinffeine events produced
Report connection status to the bitcoin network
Merge pull request #134 from sortega/task/153_bitcoin

Report status of Bitcoin Network connectivity
Add support for status bar widgets
Add a control for displaying connection as a colored disc
Renaming Downloaded to NotDownloading

The later is more accurate
Add a widget for bitcoin connection status
Integrate Bitcoin connection status on the status bar
Fix bitcoinj active connections tracking
Avoid text “1 peers” on the status bar
Merge pull request #135 from sortega/task/connection_widget

Add a bitcoin connection status widget
Add support for precision on currency.
Add an Okpay fee calculator
Add support for fees on okpaymock.
Remove compiling warning
Merge pull request #136 from gotoalberto/feesfix

Add support for fees