Update the ui

1.put Bootstrap style in bc.css
2.update the index.php to make the ui display more friendly.

By the way, i'm a peercoin supporter,glad to do some contribution to develop some application on peercoin.

May be we can provide some usefule api on PeercoinBlockExplorer in the future,that other people can get the peercoin infoation online expediently.  And thanks your remind @FuzzyBearBTC