Fixed NullPointerException if no files in root external storage
List item click opens new activity.
removed unused action bar related stuff
Added Service stub
Implement Service that plays music and allow control over palyback(pause, play)
Stop/Start button now make actions over playback
Construction of directory list is made in different thread because this operation can be slow (depends on number of files on SD card)
If app become visible, it plays music from previous position
if app just being started, it plays music from the beginning
Display progressbar while loading list of directories
refactor and clean up