Added play function

When you click the button, preview mp3 plays. But it does not stop, and it doesn't pause.
pause functionality and add button now changes

Fixed the play/pause so now it pauses also and they don't conflict,
and added the button change. Active when we have a song loaded, and
swaps playing/not playing.
Merge pull request #3 from buzzlightyear182/play-it

Play/pause functionality