Allow PoS mining reward address to be a alias

[cryptozoidberg]

The simplewallet doesn't allow us to set zano alias as an address, this should be supported (and i haven't tested an integrated address) but every address types should be supported.

This is also true for the other issues i've posted over adding the PoS mining reward address into the GUI wallet.

Thanks for checking into this!

Sumited by @Gigabyted

Moved from hyle-team/zano#263