Re-think directories structure of the wallet

[aglkm]

As suggested on grin forum:
"A minor suggestion to re-work directories structure of this wallet, it’s a bit messy in my “.grin” directory now as I have cli wallet and node too."

Either a separate ".grin-gui" directory or a separate directory inside ".grin", e.g. ".grin/main/gui".

[noobvie]

I hope we could have a wizard during the installation something like:

1. select the directory for chain_data for node
2. select the directory for wallet to store the seed