Add more features to the Coin Control menu

[ezredd]

The Coin Control menu is a very nice feature that can allow people to understand in greater detail how their wallet is staking.

I would like to add the following features so that people understand what is their total and average weight

1. add a "Coin-age" column so that each group of coins is easily associated with its posv weight
2. perhaps unhide the column that contains tx id of the group
3. maybe add an "export" feature to dump this into csv format.

I understand that those features are not necessary for the wallet to function however i believe it would have beneficial pedagogical impact especially since i intend to advertise them in the "Understanding POSV" page

http://agroff.github.io/posv/