Adds the percentage/weight of Altcoin in portfolio

This adds a little percentage-text under the altcoin logo to show the altcoin's percentage from the total portfolio. I found this very handy.

I am new to Android programming, and maybe it is possible to use the currentPortfolioValue = getCurrentPortfolioValue(); which was already called for the total balance overview before, instead of calling it again for each altcoin! Suggestions for optimizations are welcome.