Fixes #13483

The address in the network peer table is prefixed with an up-arrow symbolizing an outbound connection, or an down-array symbolizing an inbound connection. See screenshot.

The user has an easy visual confirmation about the connection direction state. I really like it :)
Impact to columns sorting is grouping by inbound/outbound first, which in my opinion is an advantage, too.
![bildschirmfoto](https://user-images.githubusercontent.com/8447873/41862752-13803eb2-78a5-11e8-9126-a52385f5ec19.png)

ninja all
./qt/bitcoin-qt -testnet