Add setting to change the inflation destination

Add a setting that shows and changes the inflation destination.

Fixes #596.

TODO: Federate the default inflation address.
At the time ```app-controller```'s ```setInflation()``` seemed like it was doing something special, but I guest the part of the function that actually builds the transaction is the same.

Should it be extracted into a ```$scope``` method in ```app-controller``` that is inherited?