Swipe improvements

This MR contains two things:

1. Scrolling through the list of transactions when putting the finger on the date or amount is now possible.
2. A swipe action is only executed when half of the action is displayed. It was not clear visually that before that half, nothing would happen. Now the background is a bit different (so we know we are swiping) but the action becomes blue or red only once half of it is shown. Behaviour shamelessly copied from K9-mail.
3. Add short text to the actions