Use JSON API of BitcoinCharts to get chart-data

There is an inofficial API available here:

bitcoincharts.com/charts/chart.json?m=mtgoxUSD&r=10

it can be used to get prefiltered and ordered data which is required to build an easy chart with the trade history.

I'm sorry for the bad quality of this commit, but I currently can't find time to rebuild it :(

I mainly extended the BitcoinCharts.java file to support the new url and added an Adapter and matching java-bean for the data.