Generate an example address (with invalid CRC) for in the bitcoin address widgets, based on the network prefix, instead of hardcoding a mainnet address.
Generates:
1NS17iag9jJgTHD1VXjvLCEnZuQ3rJDE9Lfor mainnet (same as now)n2wxQmfexkjwEPgdD6iJA7T7RtzkmHxhFcfor testnet
Later on we may get rid of the example address completely, but that's too late for 0.13, as removing e.g. %1 would change a translation string.
Testnet
